msm: mhi_dev: Update sequence when ipa_mhi_destroy is issued

Currently ipa_mhi_destroy() is issued during MHI device reset.
There could be a condition where the switch to M0 event is
in progress while the MHI device reset is received. Calling
ipa_mhi_destroy() followed by processing the M0 transition
causes IPA to assert since ipa_mhi_destroy() was already
issued. Therefore flush the workqueue that is processing
the switch to M0 transition before calling ipa_mhi_destroy().

Change-Id: I298fdc67cb5d660ba8b722016a0b4d9deb32142a
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>