drm/amdgpu: Fix locking bugs in error paths

drm/amdgpu: Fix locking bugs in error paths

Do not unlock psp->ras_context.mutex if it has not been locked. This has
been detected by the Clang thread-safety analyzer.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: YiPeng Chai <YiPeng.Chai@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Fixes: b3fb79cda568 ("drm/amdgpu: add mutex to protect ras shared memory")
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>