Fix compile error when OSS_DEBUG is enabled:
sound/core/oss/pcm_oss.c: In function 'snd_pcm_oss_set_trigger':
sound/core/oss/pcm_oss.c:2055:10: error: 'substream' undeclared (first
use in this function); did you mean 'csubstream'?
pcm_dbg(substream->pcm, "pcm_oss: trigger = 0x%x\n", trigger);
^