app: fix build with GCC 4.8

GCC 4.8 was producing this error:
	argument to ‘sizeof’ in ‘strncmp’ call is the same expression as the
	second source; did you mean to provide an explicit length?
	[-Werror=sizeof-pointer-memaccess]

Signed-off-by: Intel

app/test/test_cmdline_string.c

@@ -383,7 +383,7 @@ test_parse_string_valid(void)
 			return -1;
 		}
 		if (strncmp(buf, string_elt_strs[i].result,
-				sizeof(string_elt_strs[i].result)) != 0) {
+				sizeof(buf)) != 0) {
 			printf("Error: result mismatch!\n");
 			return -1;
 		}