ibmvnic: Do not disable IRQ after scheduling tasklet

Since the primary CRQ is only used for service functions and
not in the performance path, simplify the code a bit and avoid
disabling the IRQ.

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