SDL: Fixed warning building on iOS

SDL Commits
1 
From bff307c4b24961cc43a500a9d498181a73a0066d Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Wed, 22 Feb 2023 21:52:56 -0800
Subject: [PATCH] Fixed warning building on iOS

---
 src/joystick/apple/SDL_mfijoystick.m | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/joystick/apple/SDL_mfijoystick.m b/src/joystick/apple/SDL_mfijoystick.m
index 6d3a001137a1..4a9f732fa37b 100644
--- a/src/joystick/apple/SDL_mfijoystick.m
+++ b/src/joystick/apple/SDL_mfijoystick.m
@@ -272,6 +272,8 @@ static BOOL IOS_AddMFIJoystickDevice(SDL_JoystickDeviceItem *device, GCControlle
             /* The HIDAPI driver is taking care of this device */
             return FALSE;
         }
+#else
+        (void)is_stadia;
 #endif
 
         /* These buttons are part of the original MFi spec */