Kernel: Replace KString::must_create, fix init_args

Kernel/CommandLine.cpp

@@ -299,9 +299,9 @@ NonnullOwnPtrVector<KString> CommandLine::userspace_init_args() const
 
     auto init_args = lookup("init_args"sv).value_or(""sv).split_view(';');
     if (!init_args.is_empty())
-        MUST(args.try_prepend(KString::must_create(userspace_init())));
+        MUST(args.try_prepend(MUST(KString::try_create(userspace_init()))));
     for (auto& init_arg : init_args)
-        args.append(KString::must_create(init_arg));
+        args.append(MUST(KString::try_create(init_arg)));
     return args;
 }