linux-phytec-ti

drm: radeon: fix error value sign

enable_vblank implementations should use negative result to indicate error.
radeon_enable_vblank() returns EINVAL in this case.  Change this to -EINVAL.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>