drm/amdgpu: print bo inode number instead of ptr

This allows to correlate the infos printed by
/sys/kernel/debug/dri/n/amdgpu_gem_info to the ones found
in /proc/.../fdinfo and /sys/kernel/debug/dma_buf/bufinfo.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>