i2c: ocores: Add irq support for sparc

Add sparc support by using platform_get_irq instead of platform_get_resource.
There are no platform resources of type IORESOURCE_IRQ for sparc, but
platform_get_irq works for sparc. In the non-sparc case platform_get_irq
internally uses platform_get_resource.

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>