drm/amdgpu: fix byteorder error in amdgpu discovery

fix some byteorder issues about amdgpu discovery.
This will result in running errors on the big end system. (e.g:MIPS)

Signed-off-by: Yang Wang <KevinYang.Wang@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>