HID: i2c-hid: fix build

Add a forgotten include that I've by mistake omitted when resolving
merge conflict in ead0687fe30 ("HID: i2c-hid: support regulator power
on/off").

Fixes: ead0687fe30 ("HID: i2c-hid: support regulator power on/off")
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/i2c-hid/i2c-hid.c

@@ -38,6 +38,7 @@
 #include <linux/mutex.h>
 #include <linux/acpi.h>
 #include <linux/of.h>
+#include <linux/regulator/consumer.h>
 
 #include <linux/i2c/i2c-hid.h>