docs: Makefile: get rid of KERNELDOC_CONF env variable

Despite its name, what's there is a set of Sphinx arguments that
are passed to sphinx/kerneldoc.py:

- kerneldoc_srctree: location of the source tree;
- kerneldoc_bin: external script to excecute kernel-doc

Drop it, and just place the values at the already-existing
ALLSPHINXOPTS variable.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <88be0fc288598c30fbedb9cc230b2a7ed28225a2.1745453655.git.mchehab+huawei@kernel.org>

Author: mchehab

Documentation/Makefile

@@ -61,8 +61,8 @@ endif #HAVE_LATEXMK
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
 KERNELDOC       = $(srctree)/scripts/kernel-doc.py
-KERNELDOC_CONF  = -D kerneldoc_srctree=$(srctree) -D kerneldoc_bin=$(KERNELDOC)
-ALLSPHINXOPTS   =  $(KERNELDOC_CONF) $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
+ALLSPHINXOPTS   = -D kerneldoc_srctree=$(srctree) -D kerneldoc_bin=$(KERNELDOC)
+ALLSPHINXOPTS   += $(PAPEROPT_$(PAPER)) $(SPHINXOPTS)
 ifneq ($(wildcard $(srctree)/.config),)
 ifeq ($(CONFIG_RUST),y)
 	# Let Sphinx know we will include rustdoc