u-boot: v2026.04: helios64: avoid unaligned 8-byte read on OTP serial_num

Per CodeRabbit review on PR armbian#9675:
  *((uint64_t *) otp.serial_num) & 0xFFFFFFFFFFFF reads 8 bytes from a
  6-byte field inside a __packed__ struct (over-reads into mfg_year),
  and is unaligned. UB per the C standard, and would fault on stricter
  alignment requirements.

Same pattern affects two call sites the bot pointed at (lines 103-104
and 217-218 of the original vendor file). The bot did not flag it but
*(u16 *) otp.mfg_year on the next line has the same problem - packed
field, unaligned access - so fix it together.

Replace the casts with two small inline helpers that decode the bytes
explicitly little-endian (RK3399 is LE, matches the vendor's original
intent):

  otp_serial()    - assemble 6 bytes into a u64
  otp_mfg_year()  - assemble 2 bytes into a u16

This is pre-existing Kobol vendor code carried forward through every
U-Boot bump; this PR migrates the board files to v2026.04, so it is
the right place to fix it.

Author: iav

patch/u-boot/v2026.04/board_helios64/board/sys_otp.c

@@ -43,6 +43,26 @@ static inline int is_data_valid(void)
 	return data_valid;
 }
 
+/*
+ * Decode the 6-byte serial number into a u64. Doing a casted *(uint64_t *)
+ * read on otp.serial_num would over-read into otp.mfg_year and is unaligned
+ * inside the packed struct (UB per the C standard).
+ */
+static inline u64 otp_serial(void)
+{
+	return  ((u64)otp.serial_num[0])       |
+		((u64)otp.serial_num[1] << 8)  |
+		((u64)otp.serial_num[2] << 16) |
+		((u64)otp.serial_num[3] << 24) |
+		((u64)otp.serial_num[4] << 32) |
+		((u64)otp.serial_num[5] << 40);
+}
+
+static inline u16 otp_mfg_year(void)
+{
+	return otp.mfg_year[0] | ((u16)otp.mfg_year[1] << 8);
+}
+
 static inline int is_valid_header(void)
 {
 	static const u8 expected_magic[8] = { 'H', '6', '4', 'N', 'P', 'V', '1', 0 };
@@ -96,10 +116,9 @@ static void show_otp_data(void)
 	printf("Part Number: %s\n", otp.part_num);
 	printf("Variant: %s\n", var_str[otp.variant]);
 	printf("Revision: %x.%x\n", (otp.revision & 0xf0) >> 4, otp.revision & 0x0f);
-	printf("Serial Number: %012llx\n", *((uint64_t*) otp.serial_num) &
-		0xFFFFFFFFFFFF);
+	printf("Serial Number: %012llx\n", otp_serial());
 	printf("Manufacturing Date: %02X-%02X-%04X (DD-MM-YYYY)\n", otp.mfg_day,
-		otp.mfg_month, *(u16*) otp.mfg_year);
+		otp.mfg_month, otp_mfg_year());
 
 	printf("1GbE MAC Address:   %02X:%02X:%02X:%02X:%02X:%02X\n",
 		otp.mac_addr[0][0], otp.mac_addr[0][1], otp.mac_addr[0][2],
@@ -210,8 +229,7 @@ void set_board_info(void)
 	snprintf(env_str, sizeof(env_str), "%i.%i", (otp.revision & 0xf0) >> 4, otp.revision & 0x0f);
 	env_set("board_rev", env_str);
 
-	sprintf(env_str, "%012llx", *((uint64_t*) otp.serial_num) &
-		0xFFFFFFFFFFFF);
+	sprintf(env_str, "%012llx", otp_serial());
 
 	env_set("serial#", env_str);
 }