cifs: remove remaining build warnings

Removed remaining warnings related to externs.  These warnings
although harmless could be distracting e.g.

 fs/cifs/cifsfs.c: note: in included file:
 fs/cifs/cifsglob.h:1968:24: warning: symbol 'sesInfoAllocCount' was not declared. Should it be static?

Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>