ibmvnic: Initialize completion variables before starting work

Initialize condition variables prior to invoking any work that can
mark them complete. This resolves a race in the ibmvnic driver where
the driver faults trying to complete an uninitialized condition
variable.

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