Correct member type for struct MTSlotInfo

As pointed out by djkurtz@ in a related code review here
https://gerrit.chromium.org/gerrit/#/c/37987/2/x11-drivers/xf86-input-evdev/files/evdev-2.7.3-Add-SYN_DROPPED-handling.patch

EVIOCGMTSLOTS() takes a struct defined as
struct input_mt_request_layout {
      __u32 code;
      __s32 values[num_slots];
};

MTSlotInfo needs to explicitly make code unsigned 32bit and values array
of signed 32bit.

BUG=chromium-os:37778
TEST=compile.

Change-Id: If32ffcc7efea5e79062465967c40bd04456b4538
Reviewed-on: https://gerrit.chromium.org/gerrit/40641
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Commit-Queue: Yufeng Shen <miletus@chromium.org>
Tested-by: Yufeng Shen <miletus@chromium.org>
diff --git a/include/libevdev/libevdev_mt.h b/include/libevdev/libevdev_mt.h
index cf1cc92..df3e1c8 100644
--- a/include/libevdev/libevdev_mt.h
+++ b/include/libevdev/libevdev_mt.h
@@ -8,6 +8,7 @@
 #ifndef _LIBEVDEV_MT_H_
 #define _LIBEVDEV_MT_H_
 
+#include <stdint.h>
 #include <libevdev/libevdev_log.h>
 
 /*
@@ -24,8 +25,8 @@
 #define MAX_SLOT_COUNT  64
 
 typedef struct {
-    unsigned code;
-    int values[MAX_SLOT_COUNT];
+    uint32_t code;
+    int32_t values[MAX_SLOT_COUNT];
 } MTSlotInfo, *MTSlotInfoPtr;
 
 typedef struct {