drm/radeon: squash lines for simple wrapper functions

Remove unneeded variables and assignments.

Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1473863952-7658-3-git-send-email-yamada.masahiro@socionext.com