stagefright: Fix OmxInfoBuilder assignment of kFlagIsHardwareAccelerated

OmxInfoBuilder would only add kFlagIsHardwareAccelerated to attr if
attribute::software-code exists in the node attributes

This change inverts this logic

Author: Michael Gonzalez <michgonz@codeaurora.org>

CRs-Fixed: 2430504
Bug: 132939417
Change-Id: I9813098c062732b2a992350d72d59e52fd67292b