rfkill: fix compiler warning [-Wformat=]

* `RFKILL_EVENT_SIZE_V1` is defined as sizeof(struct rfkill_event), so let's use %zu

* cast `len` to size_t to make it usable with %zu

Signed-off-by: Karel Zak <kzak@redhat.com>

sys-utils/rfkill.c

@@ -218,7 +218,8 @@ static int rfkill_read_event(int fd, struct rfkill_event *event)
 	}
 
 	if (len < RFKILL_EVENT_SIZE_V1) {
-		warnx(_("wrong size of rfkill event: %zu < %d"), len, RFKILL_EVENT_SIZE_V1);
+		warnx(_("wrong size of rfkill event: %zu < %zu"),
+				(size_t) len, RFKILL_EVENT_SIZE_V1);
 		return 1;
 	}