f2fs: move release of block devices to after kill_block_super()

Call destroy_device_list() and free the f2fs_sb_info from
kill_f2fs_super(), after the call to kill_block_super().  This is
necessary to order it after the call to fscrypt_destroy_keyring() once
generic_shutdown_super() starts calling fscrypt_destroy_keyring() just
after calling ->put_super.  This is because fscrypt_destroy_keyring()
may call into f2fs_get_devices() via the fscrypt_operations.

Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20231227171429.9223-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>