sh: Update SE7712 PCLK definition.

This patch provides a correct value for CONFIG_SH_PCLK_FREQ for the
SH7712 solution engine when used with the board's default factory
settings. This results in the board running at its maximum CPU clock
rate (200 MHz).

Signed-off-by: Andrew Murray <amurray@mpc-data.co.uk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>