ARM: realview: convert pl061 no irq to 0 instead of -1

Drivers should use 0 for no irq, so convert realview platforms pl061
platform_data over to use 0.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: Russell King <linux@arm.linux.org.uk>