media: ti: j721e-csi2rx: Fix NULL vs IS_ERR() bug in ti_csi2rx_request_max_ppc()

The media_entity_remote_source_pad_unique() function never returns NULL,
it returns error pointers. Change this check from a NULL check to an
IS_ERR() check.

Fixes: 31f91c5224cd ("media: ti: j721e-csi2rx: Support multiple pixels per clock")
Cc: [e-mail]
Signed-off-by: Dan Carpenter <[e-mail]>
Reviewed-by: Jai Luthra <[e-mail]>
Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/platform/ti/j721e-csi2rx/j721e-csi2rx.c

···
 	int ret;
 
 	pad = media_entity_remote_source_pad_unique(&csi->vdev.entity);
-	if (!pad)
+	if (IS_ERR(pad))
 		return;
 
 	ret = cdns_csi2rx_negotiate_ppc(csi->source, pad->index, &ppc);