can: rcar_can: print request_irq() error code

Also print the error code when the request_irq() call fails in rcar_can_open(),
rewording  the error message...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>