stm32mp1: update sysconf_init on misc_read result

Update management of misc_read in sysconf_init, which now return
length of data after the commit 8729b1ae ("misc: Update read()
and write() methods to return bytes xfered")
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>

board/st/stm32mp1/stm32mp1.c

@@ -487,7 +487,7 @@ static void sysconf_init(void)
 		}
 
 		ret = misc_read(dev, STM32_BSEC_SHADOW(18), &otp, 4);
-		if (!ret)
+		if (ret > 0)
 			otp = otp & BIT(13);
 
 		/* get VDD = vdd-supply */