fs: fix new splice.c kernel-doc warning

Fix new kernel-doc warning in fs/splice.c:

  Warning(fs/splice.c:1298): No description found for parameter 'opos'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/splice.c

@@ -1283,6 +1283,7 @@ static int direct_splice_actor(struct pipe_inode_info *pipe,
  * @in:		file to splice from
  * @ppos:	input file offset
  * @out:	file to splice to
+ * @opos:	output file offset
  * @len:	number of bytes to splice
  * @flags:	splice modifier flags
  *