Input: mark custom_data in ff_periodic_effect as __user

The custom_data pointer in ff_periodict_effect structure is a
userspace pointer and should be marked as such.
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

include/linux/input.h

@@ -890,7 +890,7 @@ struct ff_periodic_effect {
 	struct ff_envelope envelope;
 
 	__u32 custom_len;
-	__s16 *custom_data;
+	__s16 __user *custom_data;
 };
 
 /**