tree 24abfd679aeb4a06d6a040704452b8e8bf68bcc6
parent 642d8b60264aacefdcba56056d0181f1cff0d2a6
author Leonardo Sandoval <leonardo.sandoval@linaro.org> 1599847993 -0500
committer Leonardo Sandoval <leonardo.sandoval@linaro.org> 1601042304 -0500

docs/Makefile: use conditional assignment on sphinx variables

If 'makefile' variables are expected to be overwritten by environment
and/or command line, it is better to use conditional assignment ('?=')
so it clearly indicates the variable intention and usage.

Change-Id: I890f71fe4bb26b5777b49e9904a1489ca8fad498
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>