drm/amdgpu/display: fix ref count leak when pm_runtime_get_sync fails

[ Upstream commit f79f94765f8c39db0b7dec1d335ab046aac03f20 ]

The call to pm_runtime_get_sync increments the counter even in case of
failure, leading to incorrect ref count.
In case of failure, decrement the ref count before returning.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>