drm/amdgpu: add reference for **fence

fix fence is released when pass to **fence sometimes.
add reference for it.

Signed-off-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian K?nig <christian.koenig@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/cik_sdma.c b/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
index c3ed5b2..2b4242b 100644
--- a/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
+++ b/drivers/gpu/drm/amd/amdgpu/cik_sdma.c
@@ -669,6 +669,7 @@
 	}
 
 err1:
+	fence_put(f);
 	amdgpu_ib_free(adev, &ib);
 err0:
 	amdgpu_wb_free(adev, index);