net/sonic: Fix a resource leak in an error handling path in 'jazz_sonic_probe()'

A call to 'dma_alloc_coherent()' is hidden in 'sonic_alloc_descriptors()',
called from 'sonic_probe1()'.

This is correctly freed in the remove function, but not in the error
handling path of the probe function.
Fix it and add the missing 'dma_free_coherent()' call.

While at it, rename a label in order to be slightly more informative.

Fixes: efcce839

 ("[PATCH] macsonic/jazzsonic network drivers update")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>