create_pipe_files(): use fput() if allocation of the second file fails

... just use put_pipe_info() to get the pipe->files down to 1 and let
fput()-called pipe_release() do freeing.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>