jffs2: move jffs2_xattr_handlers to .rodata

This makes it harder for accidental or malicious changes to
jffs2_xattr_handlers at runtime.

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-16-wedsonaf@gmail.com


Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>