smb: client: remove redudant assignment in cifs_strict_fsync()

Remove redudant assignment of @rc as it will be overwritten by the
following cifs_file_flush() call.

Reported-by: Steve French <stfrench@microsoft.com>
Addresses-Coverity: 1665925
Fixes: 210627b0aca9 ("smb: client: fix missing timestamp updates with O_TRUNC")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>