Fixes: #9453
Issue link: https://github.com/spring-projects/spring-integration/issues/9453
On a smb file upload, to detect the need for new remote directories,
the remote path was checked for the local filesystem path separator.
On Windows that is \\ which is never found in a smb path, so the
necessary remote path was not created and the operation failed.
Use the correct separator which was already available as a constant.
(cherry picked from commit 4cccee7c3a)