pcm_file: fixed memory leak.

pcm_file: fixed memory leak.

Valgrind report for this leak was:

Command: aplay -Dfile:'/tmp/qqq',raw qqq.wav

14 bytes in 1 blocks are definitely lost in loss record 1 of 2
   at 0x402BF5C: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
   by 0x40D7557: snd_pcm_file_hw_params (in /usr/lib/libasound.so.2.0.0)
   by 0x40BA093: _snd_pcm_hw_params_internal (in /usr/lib/libasound.so.2.0.0)
   by 0x40AB831: snd_pcm_hw_params (in /usr/lib/libasound.so.2.0.0)
   by 0x804C523: ??? (in /usr/bin/aplay)
   by 0x804E5B7: ??? (in /usr/bin/aplay)
   by 0x804FC8C: ??? (in /usr/bin/aplay)
   by 0x80520FB: ??? (in /usr/bin/aplay)
   by 0x4184942: (below main) (libc-start.c:226)

Signed-off-by: Andrey Mazo <mazo@telum.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>