drm/ssd130x: Fix screen clearing

drm/ssd130x: Fix screen clearing

[ Upstream commit 4dbce3d6fea59e1df1d1a35aacea0c186f72107a ]

Due to the reuse of buffers, ssd130x_clear_screen() no longers clears
the screen, but merely redraws the last image that is residing in the
intermediate buffer.

As there is no point in clearing the intermediate buffer and transposing
an all-black image, fix this by just clearing the HW format buffer, and
writing it to the panel.

Fixes: 49d7d581ceaf4cf8 ("drm/ssd130x: Don't allocate buffers on each plane update")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c19cd5a57205597bb38a446c3871092993498f01.1692888745.git.geert@linux-m68k.org
Signed-off-by: Sasha Levin <sashal@kernel.org>