gianfar: fix compile fail for NET_POLL=y due to struct packing

Commit ee873fda ("gianfar: Pack struct
gfar_priv_grp into three cachelines") moved the irq number and names
off into a separate struct and created accessors for them.  However
it was never tested with NET_POLL enabled, and so some conversions
that were simply overlooked went undetected until now.

Make the netpoll ones also use the gfar_irq() accessors.

Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Claudiu Manoil <claudiu.manoil@freescale.com>
Cc: Jianhua Xie <jianhua.xie@freescale.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>