drm/amd/amdgpu/amdgpu_ids: Supply missing docs for 'id' and 'vmhub'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:271: warning: Function parameter or member 'id' not described in 'amdgpu_vmid_grab_reserved'
 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:523: warning: Function parameter or member 'vmhub' not described in 'amdgpu_vmid_reset'

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c

@@ -259,6 +259,7 @@ static int amdgpu_vmid_grab_idle(struct amdgpu_vm *vm,
  * @sync: sync object where we add dependencies
  * @fence: fence protecting ID from reuse
  * @job: job who wants to use the VMID
+ * @id: resulting VMID
  *
  * Try to assign a reserved VMID.
  */
@@ -514,6 +515,7 @@ void amdgpu_vmid_free_reserved(struct amdgpu_device *adev,
  * amdgpu_vmid_reset - reset VMID to zero
  *
  * @adev: amdgpu device structure
+ * @vmhub: vmhub type
  * @vmid: vmid number to use
  *
  * Reset saved GDW, GWS and OA to force switch on next flush.