drm/drm_crtc: return -EFAULT on copy_to_user errors

copy_from_user() returns the number of bytes left to be copied but we
want to return a negative error code here.  This is in the ioctl handler
so the error code get returned to userspace.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>