[ARM] 4412/1: S3C2412: reset errata fix

The S3C2412 has an reset-errata where the clock
may cause a glitch switching back to EXTCLK. We
force a switch to EXTCLK before writing the
reset register to force use of the CLKCON sync
logic to properly switch.

Fix problem reported by Matthieu Castet.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>