cs89x0: fix warning release_irq label

release_irq label is only used when ALLOW_DMA is defined.

drivers/net/cs89x0.c: In function 'net_open':
drivers/net/cs89x0.c:1401: warning: label 'release_irq' defined but not used

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>