amd/amdkfd: remove unused parameter

The adev can be found from bo by amdgpu_ttm_adev(bo->tbo.bdev),
and adev is also not used in the function
amdgpu_amdkfd_map_gtt_bo_to_gart().

Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>