ocfs2: fix SGID not inherited issue

ocfs2: fix SGID not inherited issue

Oracle-bug: 22311520

commit 8f1eb48758aa ("ocfs2: fix umask ignored issue") introduced an issue,
SGID of sub dir was not inherited from its parents dir. It is because SGID
is set into "inode->i_mode" in ocfs2_get_init_inode(), but is overwritten
by "mode" which don't have SGID set later.

Fixes: 8f1eb48758aa ("ocfs2: fix umask ignored issue")
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Cc: <stable@vger.kernel.org>
Acked-by: Srinivas Eeda <srinivas.eeda@oracle.com>