serial: sh-sci: Remove duplicate interrupt check in verify port op

The driver checks if the interrupt number is greater than nr_irqs and
returns an error in that case. The same check is already performed by
the caller, remove it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>