drm/mgag200: Fix gamma lut not initialized for G200ER, G200EV, G200SE

commit 11f9eb89 upstream.

When mgag200 switched from simple KMS to regular atomic helpers,
the initialization of the gamma settings was lost.
This leads to a black screen, if the bios/uefi doesn't use the same
pixel color depth.
This has been fixed with commit ad81e234 ("drm/mgag200: Fix gamma
lut not initialized.") for most G200, but G200ER, G200EV, G200SE use
their own version of crtc_helper_atomic_enable() and need to be fixed
too.

Fixes: 1baf9127

 ("drm/mgag200: Replace simple-KMS with regular atomic helpers")
Cc: <stable@vger.kernel.org> #v6.1+
Reported-by: Roger Sewell <roger.sewell@cantab.net>
Suggested-by: Roger Sewell <roger.sewell@cantab.net>
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20231214163849.359691-1-jfalempe@redhat.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>