sh: Change register name SCSPTR to SCSPTR2

This change a name of SCSPTR used in sci_rxd_in of SH5-101.
SCSPTR is not declared and will become the error.

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