msm: gsi: fix IPC low priority logging

Allocate IPC low priority on first usage only.

Change-Id: Ic44f5af02d1d7fd72b255c8989cfc6b7dcd7766d
CRs-Fixed: 2016076
Acked-by: Ady Abraham <adya@qti,qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>