[iOS] Fix compile guard

Use proper compile guard to check for building with Xcode 12.

Bug: None
Change-Id: I782c101380565ca87b82bf574492422a57d70b3b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2269763
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Mike Dougherty <michaeldo@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782888}

ios/chrome/browser/ui/tab_grid/tab_grid_mediator.mm

@@ -447,7 +447,7 @@ web::WebState* GetWebStateWithId(WebStateList* web_state_list,
   if ([itemProvider canLoadObjectOfClass:[NSURL class]]) {
     // The parameter type has changed with Xcode 12 SDK.
     // TODO(crbug.com/1098318): Remove this once Xcode 11 support is dropped.
-#if defined(__IPHONE_14_0)
+#if defined(__IPHONE_14_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_14_0
     using providerType = __kindof id<NSItemProviderReading>;
 #else
     using providerType = id<NSItemProviderReading>;