If vmalloc() fails then we need to a bit of cleanup before returning.

Cc: <stable@vger.kernel.org>
Fixes: fb1d9738 ("drm/vmwgfx: Add DRM driver for VMware Virtual GPU")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>