Fix BufferItemConsumer::releaseBuffer error logging

STALE_BUFFER_SLOT is a hint, not an error, and shouldn't
be logged.

Fixes: 77483431
Test: verified
CtsUiRenderingTestCases:.testclasses.HardwareBitmapTests#testCreateFromPicture
doesn't log any errors to logcat

Change-Id: I570c585b7c55c668d994bf37854a2252b09b9da8