u-boot: v2026.04: helios64: add ensure_otp_data_ready() to get_revision()

Same defensive pattern as get_variant(): a transient early OTP read
failure would leave otp.valid=false, causing get_revision() to return
-1 without ever retrying. Route through ensure_otp_data_ready() so a
late-booting SPI controller gets a second chance.

Suggested-by: coderabbitai[bot] <coderabbitai[bot]@users.noreply.github.com>

Author: iav

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

@@ -218,7 +218,7 @@ int read_otp_data(void)
 
 int get_revision(int *major, int *minor)
 {
-	if (!is_data_valid())
+	if (ensure_otp_data_ready())
 		return -1;
 
 	*major = (otp.revision & 0xf0) >> 4;