platform/x86: apple-gmux: use resource_size() with res

This should be (res->end - res->start + 1) here actually,
use resource_size() derectly.
Signed-off-by: Wang Qing <wangqing@vivo.com>
Link: https://lore.kernel.org/r/1639484316-75873-1-git-send-email-wangqing@vivo.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/apple-gmux.c

@@ -625,7 +625,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
 	}
 
 	gmux_data->iostart = res->start;
-	gmux_data->iolen = res->end - res->start;
+	gmux_data->iolen = resource_size(res);
 
 	if (gmux_data->iolen < GMUX_MIN_IO_LEN) {
 		pr_err("gmux I/O region too small (%lu < %u)\n",