jack: Fixing a small memory leak

jack: Fixing a small memory leak

A small memory leak can be observed when using alsa-plugins (jack).
Check the following valgrind log:
...
==1034== 8 bytes in 1 blocks are definitely lost in loss record 7 of 108
==1034==    at 0x4027E5A: calloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==1034==    by 0x4035102: snd_pcm_jack_prepare (in /usr/lib/alsa-lib/libasound_module_pcm_jack.so)
==1034==    by 0x40D07AB: snd_pcm_ioplug_prepare (pcm_ioplug.c:145)
==1034==    by 0x4084961: snd_pcm_prepare (pcm.c:1052)
==1034==    by 0x409DDB4: snd_pcm_plugin_prepare (pcm_plugin.c:162)
==1034==    by 0x4084961: snd_pcm_prepare (pcm.c:1052)
==1034==    by 0x409DDB4: snd_pcm_plugin_prepare (pcm_plugin.c:162)
==1034==    by 0x4084961: snd_pcm_prepare (pcm.c:1052)
==1034==    by 0x4084A1D: snd_pcm_hw_params (pcm.c:838)
==1034==    by 0x4090013: snd_pcm_set_params (pcm.c:8053)
==1034==    by 0x80486EB: main (in /root/pcm_min_ok)
...
==1034== LEAK SUMMARY:
==1034==    definitely lost: 8 bytes in 1 blocks
==1034==    indirectly lost: 0 bytes in 0 blocks
==1034==      possibly lost: 31,311 bytes in 1,630 blocks
==1034==    still reachable: 5,619 bytes in 24 blocks
==1034==         suppressed: 0 bytes in 0 blocks
...

Signed-off-by: Valentin Corfu <corfuvalentin@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>