kunit: debugfs: Use IS_ERR() for alloc_string_stream() error check

The alloc_string_stream() function only returns ERR_PTR(-ENOMEM) on
failure and never returns NULL. Therefore, switching the error check in
the caller from IS_ERR_OR_NULL to IS_ERR improves clarity, indicating
that this function will return an error pointer (not NULL) when an
error occurs. This change avoids any ambiguity regarding the function's
return behavior.

Link: https://lore.kernel.org/lkml/Zy9deU5VK3YR+r9N@visitorckw-System-Product-Name
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: visitorckw

lib/kunit/debugfs.c

@@ -181,15 +181,15 @@ void kunit_debugfs_create_suite(struct kunit_suite *suite)
 	 * successfully.
 	 */
 	stream = alloc_string_stream(GFP_KERNEL);
-	if (IS_ERR_OR_NULL(stream))
+	if (IS_ERR(stream))
 		return;
 
 	string_stream_set_append_newlines(stream, true);
 	suite->log = stream;
 
 	kunit_suite_for_each_test_case(suite, test_case) {
 		stream = alloc_string_stream(GFP_KERNEL);
-		if (IS_ERR_OR_NULL(stream))
+		if (IS_ERR(stream))
 			goto err;
 
 		string_stream_set_append_newlines(stream, true);