regcomp.c: Slight optimization

regcomp.c: Slight optimization

A swash is accessed either through its inversion list or its hash (only
large swashes actually have hashes; this is usually transparent).  At
this point in regcomp.c, we only will be looking at the inversion list;
by telling swash_init function that via the flag, later accesses
automatically have a level of indirection removed.