drm/radeon: Original Radeons had PCI GART, not PCIe GART.

Just a cosmetic fix to make dmesg a little less confusing.

Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>