drm/ast: Load lut in crtc_commit

In the past the ast driver relied upon the fbdev emulation helpers to
call ->load_lut at boot-up. But since

commit b8e2b019
Author: Peter Rosin <peda@axentia.se>
Date:   Tue Jul 4 12:36:57 2017 +0200

    drm/fb-helper: factor out pseudo-palette

that's cleaned up and drivers are expected to boot into a consistent
lut state. This patch fixes that.

Fixes: b8e2b019 ("drm/fb-helper: factor out pseudo-palette")
Cc: Peter Rosin <peda@axenita.se>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <stable@vger.kernel.org> # v4.14+
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=198123


Cc: Bill Fraser <bill.fraser@gmail.com>
Reported-and-Tested-by: Bill Fraser <bill.fraser@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>