codec2: fix C2SoftMpeg4Dec initialization and release

Bug: 74770949
Test: adb push frameworks/av/media/libstagefright/data/media_codecs_google_c2_*.xml /etc/
Test: adb push frameworks/av/media/libstagefright/data/media_codecs_google_c2.xml /etc/media_codecs_c2.xml
Test: setprop debug.stagefright.ccodec yes
Test: killall mediaserver
Test: cts-tradefed run cts -m CtsMediaTestCases -t android.media.cts.MediaCodecListTest

Change-Id: Ic259cf29970d5724f3ec81b3acbb6960747c303b