media: aspeed: Fix an error handling path in aspeed_video_probe()
A dma_free_coherent() call is missing in the error handling path of the
probe, as already done in the remove function.
In fact, this call is included in aspeed_video_free_buf(). So use the
latter both in the error handling path of the probe and in the remove
function.
It is easier to see the relation with aspeed_video_alloc_buf() this way.