ui/app: (macOS) use CFTypeRef for the view factory

The os and gl packages were separate in the past, which required
uintptr for cross-package CFTypeRefs. That's no longer needed.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/gl_macos.go

@@ -25,8 +25,8 @@ type context struct {
 }
 
 func init() {
-	viewFactory = func() uintptr {
-		return uintptr(C.gio_createGLView())
+	viewFactory = func() C.CFTypeRef {
+		return C.gio_createGLView()
 	}
 }