lib/string: use size_t for local variable in strncmp

Since the 'maxlen' parameter's type is changed to size_t, the type of
the local variable 'i' which this is compared against should also be
changed to size_t.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ibe35d3741bc6d8a16a3bad3ec27aafc30745d931
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83224
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Varshit Pandya <pandyavarshit@gmail.com>

src/lib/string.c

@@ -115,7 +115,7 @@ int strcmp(const char *s1, const char *s2)
 
 int strncmp(const char *s1, const char *s2, size_t maxlen)
 {
-	int i;
+	size_t i;
 
 	for (i = 0; i < maxlen; i++) {
 		if ((s1[i] != s2[i]) || (s1[i] == '\0'))