drm/amdgpu: Address member 'ring' not described in 'amdgpu_ vce, uvd_entity_init()'

Fixes the following:

drivers/gpu/drm/amd/amdgpu/amdgpu_vce.c:237: warning: Function parameter or member 'ring' not described in 'amdgpu_vce_entity_init'
drivers/gpu/drm/amd/amdgpu/amdgpu_uvd.c:405: warning: Function parameter or member 'ring' not described in 'amdgpu_uvd_entity_init'

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>