pipe_fs_i.h: fix kernel-doc warning

Fix kernel-doc notation warnings in pipe_fs_i.h:

  Warning(include/linux/pipe_fs_i.h:58): No description found for parameter 'buffers'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/pipe_fs_i.h

@@ -30,6 +30,7 @@ struct pipe_buffer {
  *	struct pipe_inode_info - a linux kernel pipe
  *	@wait: reader/writer wait point in case of empty/full pipe
  *	@nrbufs: the number of non-empty pipe buffers in this pipe
+ *	@buffers: total number of buffers (should be a power of 2)
  *	@curbuf: the current pipe buffer entry
  *	@tmp_page: cached released page
  *	@readers: number of current readers of this pipe