pwm: Constify OF match tables

A few drivers already annotate this properly. Make the same change for
all other OF supporting drivers.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
diff --git a/drivers/pwm/pwm-spear.c b/drivers/pwm/pwm-spear.c
index 9563599..6d99e2c 100644
--- a/drivers/pwm/pwm-spear.c
+++ b/drivers/pwm/pwm-spear.c
@@ -248,7 +248,7 @@
 	return pwmchip_remove(&pc->chip);
 }
 
-static struct of_device_id spear_pwm_of_match[] = {
+static const struct of_device_id spear_pwm_of_match[] = {
 	{ .compatible = "st,spear320-pwm" },
 	{ .compatible = "st,spear1340-pwm" },
 	{ }