drm/malidp: Use struct drm_gem_object_funcs.get_sg_table internally

drm/malidp: Use struct drm_gem_object_funcs.get_sg_table internally

The malidp driver uses GEM object functions for callbacks. Fix it to
use them internally as well.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Fixes: d6511fbc9183 ("drm/malidp: Use GEM CMA object functions")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Brian Starkey <brian.starkey@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200807111022.12117-1-tzimmermann@suse.de