libc: memset: Fix MISRA issues

MISRA complained about "0"s not being followed by an "U" (please note
my protest about this!) and about values not being explicitly compared
to 0 (fair enough).
Also use explicit pointer types.

Fix those issues to make the CI happy.

Change-Id: I4d11e49c14f16223a71c78b0fc3e68ba9a1382d3
Signed-off-by: Andre Przywara <andre.przywara@arm.com>

lib/libc/memset.c

@@ -10,19 +10,20 @@
 
 void *memset(void *dst, int val, size_t count)
 {
-	char *ptr = dst;
+	uint8_t *ptr = dst;
 	uint64_t *ptr64;
 	uint64_t fill = (unsigned char)val;
 
 	/* Simplify code below by making sure we write at least one byte. */
-	if (count == 0) {
+	if (count == 0U) {
 		return dst;
 	}
 
 	/* Handle the first part, until the pointer becomes 64-bit aligned. */
-	while (((uintptr_t)ptr & 7)) {
-		*ptr++ = val;
-		if (--count == 0) {
+	while (((uintptr_t)ptr & 7U) != 0U) {
+		*ptr = (uint8_t)val;
+		ptr++;
+		if (--count == 0U) {
 			return dst;
 		}
 	}
@@ -33,15 +34,17 @@ void *memset(void *dst, int val, size_t count)
 	fill |= fill << 32;
 
 	/* Use 64-bit writes for as long as possible. */
-	ptr64 = (void *)ptr;
-	for (; count >= 8; count -= 8) {
-		*ptr64++ = fill;
+	ptr64 = (uint64_t *)ptr;
+	for (; count >= 8U; count -= 8) {
+		*ptr64 = fill;
+		ptr64++;
 	}
 
 	/* Handle the remaining part byte-per-byte. */
-	ptr = (void *)ptr64;
-	while (count--) {
-		*ptr++ = val;
+	ptr = (uint8_t *)ptr64;
+	while (count-- > 0U)  {
+		*ptr = (uint8_t)val;
+		ptr++;
 	}
 
 	return dst;