[PATCH] genirq: fix irq flow handler uninstall

The sanity check for no_irq_chip in __set_irq_hander() is unconditional on
both install and uninstall of an handler.  This triggers false warnings and
replaces no_irq_chip by dummy_irq_chip in the uninstall case.

Check only, when a real handler is installed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Sylvain Munaut <tnt@246tNt.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>