cifs: remove bogus remapping of error in cifs_filldir()

As the FIXME points out correctly, now filldir() itself returns -EOVERFLOW if
it not possible to represent the inode number supplied by the filesystem in
the field provided by userspace.

Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>