[VOL-5545] Exclude voltha-2.4 and voltha-2.5 from multiversion build

Both branches reference the kind-voltha repository in their Makefile
OTHER_REPO_DOCS which no longer exists, causing the sphinx-multiversion
build to fail when attempting to clone it. All other voltha-* branches
do not include kind-voltha and build successfully.

Change-Id: If78ddc7a0b0afe6701648442b3818ba3afd40ac8
Signed-off-by: Serkant Uluderya <serkant.uluderya@netsia.com>
diff --git a/conf.py b/conf.py
index de2dd26..1433792 100644
--- a/conf.py
+++ b/conf.py
@@ -124,8 +124,10 @@
 # smv_tag_whitelist = disabled^ # Was = None
 smv_tag_whitelist = "disabled_a^"  # Was = None
 
-# inlcude only the branches matching master and voltha-*
-smv_branch_whitelist = r"^(master|voltha-.*)$"
+# Exclude voltha-2.4 and voltha-2.5: their Makefiles clone the kind-voltha
+# repository which no longer exists, causing multiversion builds to fail.
+# All other voltha-* branches do not reference kind-voltha and build cleanly.
+smv_branch_whitelist = r"^(master|voltha-2\.(?!4$|5$)\d.*)$"
 
 # include all remote branches
 smv_remote_whitelist = r"^.*$"