android/a2dp: Fix memory leak

android/a2dp: Fix memory leak

audio_ipc_send_rsp_full() does not free buffer passed as parameter
thus it should be freed by caller.

This fixes following Valgrind report:

==1238== 5 bytes in 1 blocks are definitely lost in loss record 22 of 54
==1238==    at 0x4896DC8: calloc (in /system/lib/valgrind/vgpreload_memcheck-arm-linux.so)
==1238==    by 0x48C5DB7: g_malloc0 (gmem.c:189)
==1238==    by 0x1150EF: bt_stream_open (a2dp.c:1177)
==1238==    by 0x1116A7: ipc_handle_msg (ipc.c:95)
==1238==    by 0x111C11: audio_watch_cb (audio-ipc.c:66)
==1238==    by 0x48BD9C7: g_io_unix_dispatch (giounix.c:166)
==1238==    by 0x48C2CCB: g_main_context_dispatch (gmain.c:2539)
==1238==    by 0x48C2ED9: g_main_context_iterate.isra.19 (gmain.c:3146)
==1238==    by 0x48C3167: g_main_loop_run (gmain.c:3340)
==1238==    by 0x10B207: main (main.c:436)