No need to return a 'fake' return value on platform_get_irq() failure.

Propagate the real error instead.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>