Fix test/IRGen/async.swift

Author: aschwaighofer

test/IRGen/async.swift

@@ -17,7 +17,7 @@ public class SomeClass {}
 public func task_future_wait(_ task: __owned SomeClass) async throws -> Int
 
 // CHECK: define{{.*}} swift{{(tail)?}}cc void @"$s5async8testThisyyAA9SomeClassCnYF"(%swift.context* swiftasync %0{{.*}}
-// CHECK-64: call swiftcc i8* @swift_task_alloc(i64 56)
+// CHECK-64: call swiftcc i8* @swift_task_alloc(i64 48)
 // CHECK: {{(must)?}}tail call swift{{(tail)?}}cc void @swift_task_future_wait(
 public func testThis(_ task: __owned SomeClass) async {
   do {