drm/drm_fb_helper: Remove unnecessary braces

Remove unnecessary braces to silence the following type of
checkpatch warnings:
WARNING: braces {} are not necessary for single statement blocks
WARNING: braces {} are not necessary for any arm of this statement

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>