[ARM] S3C24XX: Fix spare errors in pwm-clock driver

Fix the following sparse warnings in arch/arm/plat-s3c24xx/pwm-clock.c:

warning: symbol 'clk_timer_scaler' was not declared. Should it be static?
warning: symbol 'clk_timer_tclk' was not declared. Should it be static?
warning: symbol 'clk_timer_tdiv' was not declared. Should it be static?

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