ir3/analyze_ubo_ranges: Account for reserved consts better

ir3/analyze_ubo_ranges: Account for reserved consts better

It turns out that the ir3_setup_const_state() already includes reserved
consts, so we were accidentally counting it twice. This makes us use
less consts, and if there are enough reserved consts can make it go
negative and wrap around. Fix this while also making sure the previous
bug remains fixed.

Fixes: 8cb1deded60 ("ir3/analyze_ubo_ranges: Account for reserved consts")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18840>