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