Fix a memory leak.

This was caught by clang's static analyzer. Warning:
frameworks/base/media/mca/filterfw/native/core/shader_program.cpp:1031:3:
warning: Potential leak of memory pointed to by 'attrib.owned_data'
    return StoreAttribute(attrib);

Bug: None.
Test: The static analyzer no longer complains.
Change-Id: Ibef0368dfa48ba57e38019a5a3e33d5bacd847a2