HWC2: Initialize retire fence to -1

Initializing to zero will cause us to inadvertently  close fd 0.
While fd 0 (stdout) isn't used in the surfaceflinger process,
if we close it, the fd becomes available for other usages, such
as fences and ion buffers. Using it becomes problematic for some
drivers which may treat it as an invalid value.

Bug: 28640429
Test: Fixes GPU driver seeing fd of 0 and erroring
Change-Id: Ifa06472d24476edb27a4306d946eb616a15aee7a