drm: Move drm_mode_setcrtc() local re-init to failure path

Instead of always re-initializing the variables we need to clean up on
out, move the re-initialization into the branch that goes back to retry
label.

This is a lateral move right now, but will allow us to pull out the
modeset locking into common code. I kept this change separate to make
things easier to review.

Changes in v2:
- None

Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20181129150423.239081-2-sean@poorly.run