msm: ipa: fix race condition when teardown pipe

When pipe is disconnected there might be a delayed work scheduled for
buffer replenish to IPA. This may cause a race condition on replenish
data structures. This change addresses this issue by ensuring that no
work may run during pipe teardown.

Change-Id: I8a138b4bb96e7ff0506781e38bf7741397be92e4
CRs-Fixed: 979113
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>