Patch from Alessandro Zummo

nas100d_power_exit(void) gets some protection
to avoid freeing an irq when it is not appropriate to do so.

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>