genirq: Fix comment describing suspend_device_irqs()

The kerneldoc comment describing suspend_device_irqs() is currently
misleading, because generally the function doesn't really disable
interrupt lines at the chip level.  Replace it with a more accurate
one.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
LKML-Reference: <200907050022.35117.rjw@sisk.pl>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>