Add an error print to s3c24xx_register_clocks to provide more useful
information when failing to register the clock.

I belive this was originally left out due to the possibility of a
problem with low-level debugging code. However, if the low-level
debug code is not functional by now there will be a whole other set of
problems being presented to the system.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>