drm/amdgpu: Cosmetic change for calling func amdgpu_gmc_vram_location

Use function parameter mc as the second parameter of amdgpu_gmc_vram_location,
so codes look more consistent.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Christian Konig <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>