Fixed an issue when inflating too many notifications

The pool of queued asynctask was limited and should really
not be, because we might be inflating a lot views at the
same time.

Test: runtest systemui
Change-Id: I3e724985e01483531051a3e9e255faa69d2591d2
Fixes: 38261831
(cherry picked from commit ae8de8c7)