net: ethernet: sun4i-emac: Fix an error handling path in emac_probe()

A dma_request_chan() call is hidden in emac_configure_dma().
It must be released in the probe if an error occurs, as already done in
the remove function.

Add the corresponding dma_release_channel() call.

Fixes: 47869e82 ("sun4i-emac.c: add dma support")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>