renesas: missing unlock on error path

We need to unlock before returning here.

Fixes: a0d2f206 ('Renesas Ethernet AVB PTP clock driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>