kfifo: fix Error/broken kernel-doc notation

Fix kernel-doc errors and warnings in new header file kfifo.h.
Don't use kernel-doc "/**" for internal functions whose comments
are not in kernel-doc format.

kernel-doc section header names (like "Note:") must be unique
per function.  Looks like I need to document that.

  Error(include/linux/kfifo.h:76): duplicate section name 'Note'
  Warning(include/linux/kfifo.h:88): Excess function parameter 'size' description in 'INIT_KFIFO'
  Error(include/linux/kfifo.h:101): duplicate section name 'Note'
  Warning(include/linux/kfifo.h:257): No description found for parameter 'fifo'
    (many of this last type, from internal functions)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>