drm/vc4: switch to drm_*{get,put} helpers

drm/vc4: switch to drm_*{get,put} helpers

drm_*_reference() and drm_*_unreference() functions are just
compatibility alias for drm_*_get() and drm_*_put() adn should not be
used by new code. So convert all users of compatibility functions to use
the new APIs.

Signed-off-by: Cihangir Akturk <cakturk@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1501761585-11757-26-git-send-email-cakturk@gmail.com
Reviewed-by: Eric Anholt <eric@anholt.net>