ARM: S3C6410: update clk->parent when setting clock source

This ensures the clock hierarchy data structures are updated when we
change the clock source in the actual hardware registers.

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