libc: Fix some MISRA defects

No functional changes.

Change-Id: I907aa47565af2a6c435a5560041fd2b59e65c25c
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/lib/libc/puts.c b/lib/libc/puts.c
index 717b522..2a0ca11 100644
--- a/lib/libc/puts.c
+++ b/lib/libc/puts.c
@@ -10,9 +10,10 @@
 {
 	int count = 0;
 
-	while (*s) {
-		if (putchar(*s++) == EOF)
+	while (*s != '\0') {
+		if (putchar(*s) == EOF)
 			return EOF;
+		s++;
 		count++;
 	}