ibmvnic: fix missing unlock on error in __ibmvnic_reset()

Add the missing unlock before return from function __ibmvnic_reset()
in the error handling case.

Fixes: ed651a10 ("ibmvnic: Updated reset handling")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>