drm/radeon: remove 0x4243 pci id

0x4243 is a PCI bridge, not a GPU.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=33815



Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>