gianfar: Fix warning when CONFIG_PM off

CC      drivers/net/ethernet/freescale/gianfar.o
drivers/net/ethernet/freescale/gianfar.c:568:13: warning: 'lock_tx_qs'
defined but not used [-Wunused-function]
 static void lock_tx_qs(struct gfar_private *priv)
             ^
drivers/net/ethernet/freescale/gianfar.c:576:13: warning: 'unlock_tx_qs'
defined but not used [-Wunused-function]
 static void unlock_tx_qs(struct gfar_private *priv)
             ^

Reported-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>