Interrupt was constantly firing because the low_threshold was
improperly configured. The low threshold needs to be 1 less than
the number of buffers posted when the CE is fully posted. The
srng backed CE's are setup with nentries - 2 buffers as the fully
posted amount, therefore the threshold needs to be nentries - 3.
Also fixes a bug where a reused variable is not cleared. This
bug could result in the threshold being set to a garbages value.
Change-Id: Iac840bfd6677683bf2feb42d8bdbd050f42e895d
CRs-Fixed: 2090603
9b55b5fbb9