[PATCH] prism54: Free skb after disabling interrupts

The dev_kfree_skb in islpci_eth_transmit happens while irqs are still
disabled, so either dev_kfree_skb_irq needs to be used or the skb
needs to be freed after irqs have been enabled again. This patch
should fix it.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>