plat/st: Fix incorrect return value

Change the return code in boot_api.h which impacts the
authentication result.
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
Change-Id: I2c3aadb98dd261ae5ad73978fc74a8a8cfa59b82
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>

plat/st/stm32mp1/include/boot_api.h

@@ -124,7 +124,7 @@
 /* Closed = OTP_CFG0[6] */
 #define BOOT_API_OTP_MODE_CLOSED_BIT_POS			6
 
-#define BOOT_API_RETURN_OK					0x66U
+#define BOOT_API_RETURN_OK					0x77U
 
 /*
  * Boot Context related definitions