drm/amdgpu: don't oops on failure to load (v2)

In two places amdgpu tries to tear down something it hasn't
initalised when failing. This is what happens when you
enable experimental support on topaz which then fails in
ring init.

This patch allows it to fail cleanly.

v2 (agd): split out scheduler change into a separate patch
Reviewed-by: NChunming Zhou <david1.zhou@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c

@@ -69,6 +69,9 @@ void amdgpu_ctx_fini(struct amdgpu_ctx *ctx)
 	struct amdgpu_device *adev = ctx->adev;
 	unsigned i, j;
 
+	if (!adev)
+		return;
+
 	for (i = 0; i < AMDGPU_MAX_RINGS; ++i)
 		for (j = 0; j < AMDGPU_CTX_MAX_CS_PENDING; ++j)
 			fence_put(ctx->rings[i].fences[j]);