[ARM] S3C2443: Fix the S3C2443 clock register definitions

Fix the S3C2443 clock register definitions for selecting the EPLL
reference clock described by S3C2443_CLKSRC_EPLLREF.

Signed-off-by: Wei Shuai <cpuwolf@gmail.com>
[ben-linux@fluff.org: minor description fixes]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>