drm/radeon: 0x9649 is SUMO2 not SUMO

commit d00adcc8ae9e22eca9d8af5f66c59ad9a74c90ec upstream.

Fixes rendering corruption due to incorrect
gfx configuration.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=63599



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>