tools/uncrustify: Make sure a space exists after a comma.

This will add a space after a comma if it doesn't have one, but will allow
more than one space if the spaces are already there.

Signed-off-by: Damien George <damien@micropython.org>

tools/uncrustify.cfg

@@ -372,7 +372,7 @@ sp_inside_square                = ignore   # ignore/add/remove/force
 sp_inside_square_oc_array       = ignore   # ignore/add/remove/force
 
 # Add or remove space after ',', i.e. 'a,b' vs. 'a, b'.
-sp_after_comma                  = ignore   # ignore/add/remove/force
+sp_after_comma                  = add      # ignore/add/remove/force
 
 # Add or remove space before ','.
 #