drm/mga/mga_state: Remove unused variable 'buf_priv'

drm/mga/mga_state: Remove unused variable 'buf_priv'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/mga/mga_state.c: In function ‘mga_dma_iload’:
 drivers/gpu/drm/mga/mga_state.c:945:22: warning: variable ‘buf_priv’ set but not used [-Wunused-but-set-variable]

Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: by <jhartmann@precisioninsight.com>
Cc: Jeff Hartmann <jhartmann@valinux.com>
Cc: Keith Whitwell <keith@tungstengraphics.com>
Cc: Gareth Hughes <gareth@valinux.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106214949.2042120-6-lee.jones@linaro.org