ufs: add additional sync between ice work queue and pending request

Fixes the issue where the job could have been scheduled with request
that was about to be released thus causing crash with stale pointer.

Change-Id: I4ed1f08ed810303738c05d08f27a8ea21ba1e4f7
Signed-off-by: Andrey Markovytch <andreym@codeaurora.org>