ARM/LPC32xx: Use irq not hwirq for __irq_set_handler_locked()

irq_data->hwirq is not guaranteed to be the same as irq_data->irq. It
might be in that particular case, but it's wrong nevertheless.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Roland Stigge <stigge@antcom.de>