ARM: 6979/1: mach-vt8500: add forgotten irq_data conversion

This platform has not been converted to 'struct irq_data' when the big
pile was done and fails to compile nowadays. Tested on a JayPC-Tablet.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Alexey Charkov <alchark@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>