kunit: alloc_string_stream_fragment error handling bug fix

When it fails to allocate fragment, it does not free and return error.
And check the pointer inappropriately.

Fixed merge conflicts with
commit 6188877 ("kunit: update NULL vs IS_ERR() tests")
Shuah Khan <skhan@linuxfoundation.org>

Signed-off-by: YoungJun.park <her0gyugyu@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: youngjun-89

lib/kunit/string-stream.c

@@ -23,8 +23,10 @@ static struct string_stream_fragment *alloc_string_stream_fragment(
 		return ERR_PTR(-ENOMEM);
 
 	frag->fragment = kunit_kmalloc(test, len, gfp);
-	if (!frag->fragment)
+	if (!frag->fragment) {
+		kunit_kfree(test, frag);
 		return ERR_PTR(-ENOMEM);
+	}
 
 	return frag;
 }