gfs2: don't withdraw if init_threads() got interrupted

In gfs2_fill_super(), when mounting a gfs2 filesystem is interrupted,
kthread_create() can return -EINTR.  When that happens, we roll back
what has already been done and abort the mount.

Since commit 62dd0f98 ("gfs2: Flag a withdraw if init_threads()
fails), we are calling gfs2_withdraw_delayed() in gfs2_fill_super();
first via gfs2_make_fs_rw(), then directly.  But gfs2_withdraw_delayed()
only marks the filesystem as withdrawing and relies on a caller further
up the stack to do the actual withdraw, which doesn't exist in the
gfs2_fill_super() case.  Because the filesystem is marked as withdrawing
/ withdrawn, function gfs2_lm_unmount() doesn't release the dlm
lockspace, so when we try to mount that filesystem again, we get:

    gfs2: fsid=gohan:gohan0: Trying to join cluster "lock_dlm", "gohan:gohan0"
    gfs2: fsid=gohan:gohan0: dlm_new_lockspace error -17

Since commit b77b4a48

 ("gfs2: Rework freeze / thaw logic"), the
deadlock this gfs2_withdraw_delayed() call was supposed to work around
cannot occur anymore because freeze_go_callback() won't take the
sb->s_umount semaphore unconditionally anymore, so we can get rid of the
gfs2_withdraw_delayed() in gfs2_fill_super() entirely.

Reported-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: stable@vger.kernel.org # v6.5+