pwm: fsl-ftm: Handle clk_get_rate() returning 0

Considering that the driver doesn't enable the used clocks (and also
that clk_get_rate() returns 0 if CONFIG_HAVE_CLK is unset) better check
the return value of clk_get_rate() for being non-zero before dividing by
it.

Fixes: 3479bbd ("pwm: fsl-ftm: More relaxed permissions for updating period")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/b68351a51017035651bc62ad3146afcb706874f0.1743501688.git.u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

drivers/pwm/pwm-fsl-ftm.c

@@ -118,6 +118,9 @@ static unsigned int fsl_pwm_ticks_to_ns(struct fsl_pwm_chip *fpc,
 	unsigned long long exval;
 
 	rate = clk_get_rate(fpc->clk[fpc->period.clk_select]);
+	if (rate >> fpc->period.clk_ps == 0)
+		return 0;
+
 	exval = ticks;
 	exval *= 1000000000UL;
 	do_div(exval, rate >> fpc->period.clk_ps);
@@ -190,6 +193,9 @@ static unsigned int fsl_pwm_calculate_duty(struct fsl_pwm_chip *fpc,
 	unsigned int period = fpc->period.mod_period + 1;
 	unsigned int period_ns = fsl_pwm_ticks_to_ns(fpc, period);
 
+	if (!period_ns)
+		return 0;
+
 	duty = (unsigned long long)duty_ns * period;
 	do_div(duty, period_ns);