If devm_request_threaded_irq() fails, we should better propagate the real error.

Also, print out the error code in the dev_err message.
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>