fuse: check s_root when destroying sb

stable inclusion
from stable-v5.10.179
commit 0078a1667cbf7e674430186837698503f0ef4272
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8C809

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0078a1667cbf7e674430186837698503f0ef4272



--------------------------------

commit d534d31d upstream.

Checking "fm" works because currently sb->s_fs_info is cleared on error
paths; however, sb->s_root is what generic_shutdown_super() checks to
determine whether the sb was fully initialized or not.

This change will allow cleanup of sb setup error paths.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Yang Bo <yb203166@antfin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>