'ret' is known to be 0 at this point.
If 'safexcel_request_ring_irq()' fails, it returns an error code.
Return this value instead of 0 which means success.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>