doc: fix doxy for hiding internal symbols
Docyten syntax for EXCLUDE_SYMBOLS is with spaces for separator,
not commas.
@@ -866,7 +866,7 @@ EXCLUDE_PATTERNS =
# Exclude internal names (starting with an _) and doxygen-added __unnamed__
# names given to unnamed nested unions
-EXCLUDE_SYMBOLS = _*, *.__unnamed__
+EXCLUDE_SYMBOLS = _* *.__unnamed__
# The EXAMPLE_PATH tag can be used to specify one or more files or directories
# that contain example code fragments that are included (see the \include
