tmpfs: clear S_ISGID when setting posix ACLs

tmpfs: clear S_ISGID when setting posix ACLs

This change was missed the tmpfs modification in In CVE-2016-7097
commit 073931017b49 ("posix_acl: Clear SGID bit when setting
file permissions")
It can test by xfstest generic/375, which failed to clear
setgid bit in the following test case on tmpfs:

  touch $testfile
  chown 100:100 $testfile
  chmod 2755 $testfile
  _runas -u 100 -g 101 -- setfacl -m u::rwx,g::rwx,o::rwx $testfile

Signed-off-by: Gu Zheng <guzheng1@huawei.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from commit 497de07d89c1410d76a15bec2bb41f24a2a89f31)

Orabug: 24587481
CVE-2016-7097

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>