staging: erofs: fix compile error without built-in decompression support

This patch fixes incorrect code snippets due to spilt code
into small patches by mistake.

Link: https://lists.01.org/pipermail/kbuild-all/2018-July/050747.html
Link: https://lists.01.org/pipermail/kbuild-all/2018-July/050750.html


Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>