ibmvnic: Merge the two release_sub_crq_queue routines

Keeping two routines for releasing sub crqs, one for when irqs are not
initialized and one for when they are, is a bit of overkill. Merge the
two routines to a common release routine that will check for an irq
and release it if needed.

Signed-off-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>