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

Just return the error code itself instead.
Signed-off-by: NPeter Chen <peter.chen@freescale.com>
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>