media: cx18: update *pos correctly in cx18_read_pos()

We should be updating *pos.  The current code is a no-op.

Fixes: 1c1e45d1 ("V4L/DVB (7786): cx18: new driver for the Conexant CX23418 MPEG encoder chip")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/pci/cx18/cx18-fileops.c

@@ -484,7 +484,7 @@ static ssize_t cx18_read_pos(struct cx18_stream *s, char __user *ubuf,
 
 	CX18_DEBUG_HI_FILE("read %zd from %s, got %zd\n", count, s->name, rc);
 	if (rc > 0)
-		pos += rc;
+		*pos += rc;
 	return rc;
 }