drm/vmwgfx: drop dma_buf reference on foreign-fd prime import

In the Linux kernel, the following vulnerability has been resolved: drm/vmwgfx: drop dma_buf reference on foreign-fd prime import ttm_prime_fd_to_handle() returns -ENOSYS when the imported fd's dma_buf->ops do not match the ttm_object_device's ops, but does so without releasing the reference acquired by dma_buf_get(). Any unprivileged renderD client passing a non-vmwgfx prime fd through the DRM_VMW_GB_SURFACE_REF{,_EXT} path leaks one dma_buf reference per call and indefinitely pins the foreign exporter's GEM resources. Funnel the error path through the existing dma_buf_put() so the reference is always dropped.