block: row: Fix crash when adding a new field in bio struct

When adding new field to struct bio there is a crash in the removed
code lines. This issue was introduced by commit
80a8f0f8  "block: row-iosched idling
triggered by readahead pages"

(Partly) reverting this patch till root cause is fixed (on FS level).

Change-Id: Idce180802227aaab495bf0723768ba4cb437bcab
Signed-off-by: Tanya Brokhman <tlinder@codeaurora.org>