[kernel-doc] fix various DocBook build problems/warnings

Most serious is fixing include/sound/pcm.h, which breaks the DocBook
build.

The other stuff is just filling in things that cause warnings.
diff --git a/kernel/sched.c b/kernel/sched.c
index 5f889d0..f41fa94 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1478,6 +1478,7 @@
 
 /**
  * finish_task_switch - clean up after a task-switch
+ * @rq: runqueue associated with task-switch
  * @prev: the thread we just switched away from.
  *
  * finish_task_switch must be called after the context switch, paired