drm/crtc_helper/set_config: Remove redundant handling when set->fb is NULL

We've done sanity NULL pointer check on set->fb at the beginning of
drm_crtc_helper_set_config() and bailed out if necessary, thus any later on
check or case handling is redundant.

Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452751210-19216-1-git-send-email-gnuiyl@gmail.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>