video: fbdev: riva: remove some unused varibles

Couple of variables are actually useless, remove them to save some gcc
warning:
drivers/video/fbdev/riva/riva_hw.c:250:21: warning: variable ‘mlwm’ set
but not used [-Wunused-but-set-variable]
drivers/video/fbdev/riva/riva_hw.c:665:15: warning: variable ‘vraw’ set
but not used [-Wunused-but-set-variable]
drivers/video/fbdev/riva/riva_hw.c:665:9: warning: variable ‘craw’ set
but not used [-Wunused-but-set-variable]
drivers/video/fbdev/riva/riva_hw.c:659:73: warning: variable ‘align’ set
but not used [-Wunused-but-set-variable]
drivers/video/fbdev/riva/riva_hw.c:659:50: warning: variable
‘color_key_enable’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Antonino Daplas <adaplas@gmail.com>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1604822519-65607-1-git-send-email-alex.shi@linux.alibaba.com