pwm: vt8500: Fix coding style issue

Fixes the following:
WARNING: Prefer pr_warn(... to pr_warning(...
	pr_warning("Waiting for status bits 0x%x to clear timed out\n",

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>