ARM: S3C6410: use correct divider_shift in setrate_clksrc()

In s3c64xx_setrate_clksrc() we used sclk->shift, but actually need to
use sclk->divider_shift to correctly calculate the value for the divider
register.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
[ben-linux@fluff.org: Minor re-indentation of description]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>