V4L/DVB: drivers/media/video/zoran: Use available error codes

Error codes are stored in res, but the return value is always 0.  Return
res instead.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@r@
local idexpression x;
constant C;
@@

if (...) { ...
  x = -C
  ... when != x
(
  return <+...x...+>;
|
  return NULL;
|
  return;
|
* return ...;
)
}
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/zoran/zoran_driver.c

@@ -3322,7 +3322,7 @@ zoran_mmap (struct file           *file,
 mmap_unlock_and_return:
 	mutex_unlock(&zr->resource_lock);
 
-	return 0;
+	return res;
 }
 
 static const struct v4l2_ioctl_ops zoran_ioctl_ops = {