[ARM] S3C: Tidy sleep code path to fix call flow

As noted by Russell King, the sleep code path is not
elegant and makes use of leaving items on the stack
between calls.

Change the code that does the following:

        if (s3c_cpu_save(regs_save) == 0) {
                flush_cache_all();
                S3C_PMDBG("preparing to sleep\n");
                pm_cpu_sleep();
        }

to simply call s3c_cpu_save, and let that do the
necessary calls to quiesce and sleep the system.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>