skge: Unmask interrupts in case of spurious interrupts

In case of a spurious interrupt dont forget to reenable the interrupts that
have been masked by reading the interrupt source register.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Acked-by: Mirko Lindner <mlindner@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>