hwmon: (gpio-fan) 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: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/gpio-fan.c

@@ -31,6 +31,7 @@
 #include <linux/hwmon.h>
 #include <linux/gpio.h>
 #include <linux/gpio-fan.h>
+#include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/of_gpio.h>