Revert "[PATCH 3/3] staging, zram: use zs_mem_[read/write]"

This reverts commit fbb16da837095ce2bb0bd49575e7a204c5255ef5.
Revert "Fix zram_drv.c compilation error"

This reverts commit 0f43596e5a6c7547aed9c56c7b66f27525cff06a.
Revert "[PATCH 1/3] staging, zsmalloc: introduce zs_mem_[read/write]"

This reverts commit c640b887a20c3a121f9fc5e9a59f16a185e43714.