block: misc ioc cleanups

* int return from put_io_context() wasn't used by anybody.  Make it
  return void like other put functions and docbook-fy the function
  comment.

* Reorder dummy declarations for !CONFIG_BLOCK case a bit.

* Make alloc_ioc_context() use __GFP_ZERO allocation, take init out of
  if block and drop 0'ing.

* Docbook-fy current_io_context() comment.

This patch doesn't introduce any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 5037a0a..8a6ecb66 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -76,20 +76,14 @@
 
 struct task_struct;
 #ifdef CONFIG_BLOCK
-int put_io_context(struct io_context *ioc);
+void put_io_context(struct io_context *ioc);
 void exit_io_context(struct task_struct *task);
 struct io_context *get_io_context(gfp_t gfp_flags, int node);
 struct io_context *alloc_io_context(gfp_t gfp_flags, int node);
 #else
-static inline void exit_io_context(struct task_struct *task)
-{
-}
-
 struct io_context;
-static inline int put_io_context(struct io_context *ioc)
-{
-	return 1;
-}
+static inline void put_io_context(struct io_context *ioc) { }
+static inline void exit_io_context(struct task_struct *task) { }
 #endif
 
 #endif