pwm: Check for negative duty-cycle and period

Make sure the duty-cycle and period passed in are not negative. This
should eventually be made implicit by making them unsigned. While at
it, the drivers' .config() implementations can have the equivalent
checks removed.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Axel Lin <axel.lin@gmail.com>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Jonghwan Choi <jhbird.choi@samsung.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: "Philip, Avinash" <avinashphilip@ti.com>
Cc: Vaibhav Bedia <vaibhav.bedia@ti.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>

drivers/pwm/pwm-pxa.c

@@ -70,9 +70,6 @@ static int pxa_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
 	unsigned long offset;
 	int rc;
 
-	if (period_ns == 0 || duty_ns > period_ns)
-		return -EINVAL;
-
 	offset = pwm->hwpwm ? 0x10 : 0;
 
 	c = clk_get_rate(pc->clk);