[ARM] 5560/1: Avoid buffer overrun in case of an invalid IRQ

handle_bad_irq() expects the IRQ number to be valid (used for statistics),
so it cannot be called with an illegal vector. The problem was reported
by a static analysis tool.

The change makes bad_irq_desc redundant, so delete it.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>