pwm: twl: Include linux/of.h header

'of_match_ptr' is defined in linux/of.h. Include it explicitly.
Signed-off-by: NSachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: NThierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-twl.c

@@ -18,6 +18,7 @@
  */
 
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/pwm.h>
 #include <linux/i2c/twl.h>