pwm: brcmstb: Utilize appropriate clock APIs in suspend/resume

The suspend/resume functions currently utilize
clk_disable()/clk_enable() respectively which may be no-ops with certain
clock providers such as SCMI. Fix this to use clk_disable_unprepare()
and clk_prepare_enable() respectively as we should.

Fixes: 3a9f5957

 ("pwm: Add Broadcom BCM7038 PWM controller support")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>