video: pxa3xx-gcu: Return -EFAULT when copy_from_user() fails

Return -EFAULT instead of number of bytes that could not be copied if
copy_from_user() fails.

Also fix a typo in the comments.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>