jffs2: free jffs2_sb_info through jffs2_kill_sb()

jffs2: free jffs2_sb_info through jffs2_kill_sb()

When an invalid mount option is passed to jffs2, jffs2_parse_options()
will fail and jffs2_sb_info will be freed, but then jffs2_sb_info will
be used (use-after-free) and freeed (double-free) in jffs2_kill_sb().

Fix it by removing the buggy invocation of kfree() when getting invalid
mount options.

Fixes: 92abc475d8de ("jffs2: implement mount option parsing and compression overriding")
Cc: stable@kernel.org
Signed-off-by: Hou Tao <houtao1@huawei.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>