cifs: remove some minor warnings pointed out by kernel test robot

Correct some trivial warnings caused when new file unc.c
was created. For example:

   In file included from fs/cifs/unc.c:11:
>> fs/cifs/cifsproto.h:44:28: warning: 'struct TCP_Server_Info' declared inside parameter list will not be visible outside of this definition or declaration
      44 | extern int smb_send(struct TCP_Server_Info *, struct smb_hdr *,

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Steve French <stfrench@microsoft.com>