serial: sh-sci: fix overrun error handling for SH7785 SCIF.

There was a typo for the overrun bit definition, causing it not to be
handled correctly on SH7785, fix it up.

Signed-off-by: Kuninori Morimoto <morimoto.kuninori@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>