make linkcheckdocs error with 4.13-rc7

[Jim Davis]

On my Fedora 26 desktop (with Sphinx 1.6.3), make linkcheckdocs is failing with

InputError: [Errno 2] No such file or directory:
'/data/linux-rc/Documentation/output/cec.h.rst'.

reST markup error:
/data/linux-rc/Documentation/media/uapi/cec/cec-header.rst:9:
(SEVERE/4) Problems with "kernel-include" directive path:
InputError: [Errno 2] No such file or directory:
'/data/linux-rc/Documentation/output/cec.h.rst'.
make[1]: *** [Documentation/Makefile:69: linkcheckdocs] Error 1
make: *** [Makefile:1474: linkcheckdocs] Error 2

I haven't been testing that target consistently with previous -rcs,
but I think that failure is new.

-- 
Jim