drm/edid: Make edid_load() return a void *

Always use "void *" for arbitrary memory buffers, as this allows to drop
casts in assignments.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>