ARM/LPC32xx: Use irq_set_handler_locked()

Use irq_set_handler_locked() as it avoids a redundant lookup of the
irq descriptor.

Search and replacement was done with coccinelle.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org