input: align HID adapter slot type with pad_connection_pad_init

GCC on 10.5 PPC warned:

  iohidmanager_hid.c:691: warning: comparison between signed and
  unsigned

pad_connection_pad_init() at input/connect/joypad_connection.c:397
returns int32_t and can return -1 on allocation failure.  Four HID
drivers store that return value in an adapter struct field and use
it for array indexing.  Three got the type wrong:

  iohidmanager_hid.c : uint32_t slot (warning reported here)
  btstack_hid.c      : uint32_t slot (same structural mismatch,
                       silent - no == -1 check at call site)
  libusb_hid.c       : int slot      (compiles clean, but width is
                       implicit rather than explicit)
  wiiusb_hid.c       : int32_t slot  (correct)

Align all four on int32_t, matching the return type of
pad_connection_pad_init and wiiusb_hid.c's precedent.

Array-indexing call sites (hid->slots[adapter->slot], hid->hats
[adapter->slot][...], etc.) are unaffected - signed and unsigned
integer types index arrays identically through integer promotion
to ptrdiff_t.  The only behavioural effect is that slot == -1
checks (iohidmanager_hid.c:691, libusb_hid.c:313) are now signed/
signed comparisons and actually do what they look like they do.

Previously the iohidmanager check "worked" only because the
promotion rules happen to coerce (int)-1 to UINT32_MAX for the
comparison - accidental correctness.

Author: LibretroAdmin

input/drivers_hid/btstack_hid.c

@@ -681,7 +681,7 @@ struct btpad_queue_command
 
 struct btstack_hid_adapter
 {
-   uint32_t slot;
+   int32_t slot;
 
    enum btpad_state state;
 

input/drivers_hid/iohidmanager_hid.c

@@ -49,7 +49,12 @@ typedef struct apple_hid
 
 struct iohidmanager_hid_adapter
 {
-   uint32_t slot;
+   /* pad_connection_pad_init() returns int32_t and can return -1 on
+    * allocation failure.  Storing the return in uint32_t compiles
+    * but makes the `slot == -1` check at the call site a signed/
+    * unsigned comparison GCC warns about.  Matches wiiusb_hid.c's
+    * adapter struct which got this right. */
+   int32_t slot;
    IOHIDDeviceRef handle;
    uint32_t locationId;
    char name[NAME_MAX_LENGTH];

input/drivers_hid/libusb_hid.c

@@ -68,7 +68,7 @@ struct libusb_adapter
    uint8_t name[NAME_MAX_LENGTH];
    uint8_t data[2048];
 
-   int slot;
+   int32_t slot;
 
    sthread_t *thread;
    slock_t *send_control_lock;