drm/amdgpu: Fix out-of-bounds write warning

[ Upstream commit be168493 ]

Check the ring type value to fix the out-of-bounds
write warning

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>