drm: fix LOCK_TEST_WITH_RETURN macro

When this macro isn't called with 'file_priv' this will result in a build
failure.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>