board: update test on misc_read result in board_late_init

Update management of misc_read, which now return length of data
after the commit 8729b1ae ("misc: Update read() and write()
methods to return bytes xfered")

Fixes: 8b8b3d6b ("stm32mp1: board: add environment variable for board id and board rev")
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: NPatrice Chotard <patrice.chotard@st.com>

board/st/stm32mp1/stm32mp1.c

@@ -686,7 +686,7 @@ int board_late_init(void)
 	if (!ret)
 		ret = misc_read(dev, STM32_BSEC_SHADOW(BSEC_OTP_BOARD),
 				&otp, sizeof(otp));
-	if (!ret && otp) {
+	if (ret > 0 && otp) {
 		snprintf(buf, sizeof(buf), "0x%04x", otp >> 16);
 		env_set("board_id", buf);