util/ra: Sanity check that we're adding a valid reg to a class.

BITSET_SET might not segfault on you right away if you're just slightly
off, and an assert is nicer anyway.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4537>

src/util/register_allocate.c

@@ -371,6 +371,8 @@ ra_class_add_reg(struct ra_regs *regs, unsigned int c, unsigned int r)
 {
    struct ra_class *class = regs->classes[c];
 
+   assert(r < regs->count);
+
    BITSET_SET(class->regs, r);
    class->p++;
 }