sh: Fix mistake of the member variable of plat_sci_port for SH7343

The current code was going to initialize irq of plat_sci_port.
Not irq, irqs is right.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>