lib_strftime: Fix %I to avoid printing 00:xx AM/PM

Currently strftime is printing 00:00 AM and 00:00 PM instead of
12:00 AM and 12:00 PM when using %I.

This commit fixes this issue!

libs/libc/time/lib_strftime.c

@@ -267,7 +267,8 @@ size_t strftime(FAR char *s, size_t max, FAR const char *format,
 
            case 'I':
              {
-               len = snprintf(dest, chleft, "%02d", tm->tm_hour % 12);
+               len = snprintf(dest, chleft, "%02d", (tm->tm_hour % 12) != 0 ?
+                                                    (tm->tm_hour % 12) : 12);
              }
              break;