msm: ipa3: stop polling gsi on interrupt mode

When switching to interrupt mode on GSI there is no need to
poll GSI for new packets as those will be notified via callback.
Removing the poll to avoid a race condition between the poll function
and the callback function.

Change-Id: I1d7fbab6ecbee85124dfd48bd4f8b8fd3f8956e5
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>