drm/vc4: Return -EFAULT on copy_from_user() failure

The copy_from_user() function returns the number of bytes not copied but
we want to return a negative error code.

Fixes: 463873d5 ('drm/vc4: Add an API for creating GPU shaders in GEM BOs.')
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>