fix(mmc): explicitly check operators precedence

This corrects the MISRA violation C2012-12.1:
The precedence of operators within expressions should be made explicit
While at it put the test on one line.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Id19231faaf033c1e7dbe703690e0dddc7aa8f346
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 8e83464..1a63f61 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -780,8 +780,7 @@
 	unsigned char current_boot_part = mmc_current_boot_part();
 	int ret;
 
-	if (current_boot_part != 1U &&
-	    current_boot_part != 2U) {
+	if ((current_boot_part != 1U) && (current_boot_part != 2U)) {
 		ERROR("Got unexpected value for active boot partition, %u\n", current_boot_part);
 		return -EIO;
 	}