support/graph-depends: fix package names starting with a non-alpha

Graphviz' dot utility does not like nodes which names does not start
with an ^[[:alpha:]], i.e. 18xx-ti-utils would cause grievance:

    Warning: syntax ambiguity - badly delimited number '18x' in line 4 [...]/graph-depends.dot splits into two tokens
    Warning: syntax ambiguity - badly delimited number '18x' in line 5 [...]/graph-depends.dot splits into two tokens
    Warning: syntax ambiguity - badly delimited number '18x' in line 6 [...]/graph-depends.dot splits into two tokens
    Warning: syntax ambiguity - badly delimited number '18x' in line 7 [...]/graph-depends.dot splits into two tokens

Prefix nodes with an underscore to fix that.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 020206ca5784ca60fd72c7ff0aea6557d1d9bf6e)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/scripts/graph-depends

@@ -94,9 +94,10 @@ def get_all_depends(pkgs, get_depends_func):
 
 
 # The Graphviz "dot" utility doesn't like dashes in node names. So for
-# node names, we strip all dashes.
+# node names, we strip all dashes. Also, nodes can't start with a number,
+# so we prepend an underscore.
 def pkg_node_name(pkg):
-    return pkg.replace("-", "")
+    return "_" + pkg.replace("-", "")
 
 
 TARGET_EXCEPTIONS = [