pwm: Drop unused #include <linux/radix-tree.h>

core.c doens't use any of the symbols provided by linux/radix-tree.h
and compiles just fine without this include. So drop the #include.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/core.c

@@ -10,7 +10,6 @@
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/pwm.h>
-#include <linux/radix-tree.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/err.h>