pwm: imx: Include linux/of.h header

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

drivers/pwm/pwm-imx.c

@@ -16,6 +16,7 @@
 #include <linux/clk.h>
 #include <linux/io.h>
 #include <linux/pwm.h>
+#include <linux/of.h>
 #include <linux/of_device.h>
 
 /* i.MX1 and i.MX21 share the same PWM function block: */