[media] wl128x: fix compiler warning + wrong write() return

The fix is to check for ret and return -EFAULT if non-zero.

I also noticed that write() didn't return the number of bytes written.
Fixed as well.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/radio/wl128x/fmdrv_v4l2.c

@@ -84,12 +84,14 @@ static ssize_t fm_v4l2_fops_write(struct file *file, const char __user * buf,
 	ret = copy_from_user(&rds, buf, sizeof(rds));
 	fmdbg("(%d)type: %d, text %s, af %d\n",
 		   ret, rds.text_type, rds.text, rds.af_freq);
+	if (ret)
+		return -EFAULT;
 
 	fmdev = video_drvdata(file);
 	fm_tx_set_radio_text(fmdev, rds.text, rds.text_type);
 	fm_tx_set_af(fmdev, rds.af_freq);
 
-	return 0;
+	return sizeof(rds);
 }
 
 static u32 fm_v4l2_fops_poll(struct file *file, struct poll_table_struct *pts)