Revert "UPSTREAM: zram: set BDI_CAP_STABLE_WRITES once"

This reverts commit 7b4e1b64.

This is a preparation change for merging android-4.14 commit
e709f59a into msm-4.14 branch.
The reverted change is committed already as:

3694ff6b zram: set BDI_CAP_STABLE_WRITES once

Change-Id: Id7d4ac9130c4d727df64e9887993a737af98f674
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>