smb: fix bytes written value in /proc/fs/cifs/Stats

With recent netfs apis changes, the bytes written
value was not getting updated in /proc/fs/cifs/Stats.
Fix this by updating tcon->bytes in write operations.

Fixes: 3ee1a1fc ("cifs: Cut over to using netfslib")
Signed-off-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>