drivers:iio:Fix the NULL vs IS_ERR() bug for debugfs_create_dir()

The debugfs_create_dir() function returns error pointers.
It never returns NULL. So use IS_ERR() to check it.
Signed-off-by: Yang Ruibin <11162571@vivo.com>
Link: https://patch.msgid.link/20240821083911.3411-1-11162571@vivo.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-backend.c

@@ -219,7 +219,7 @@ void iio_backend_debugfs_add(struct iio_backend *back,
 	snprintf(name, sizeof(name), "backend%d", back->idx);
 
 	back_d = debugfs_create_dir(name, d);
-	if (!back_d)
+	if (IS_ERR(back_d))
 		return;
 
 	if (back->ops->debugfs_reg_access)