drm/amdgpu: Fix uninitialized variable warnings

[ Upstream commit 60c44843 ]

return 0 to avoid returning an uninitialized variable r

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