nir/constant_folding: Fix source bit size logic

nir/constant_folding: Fix source bit size logic

Instead of looking at input_sizes[i] which contains the number of
components for each source, we look at the bit size of input_types[i].
This fixes a regression in the 1-bit boolean series though I have no
idea how we haven't seen it before now.

Fixes: 35baee5dce5 "nir/constant_folding: fix incorrect bit-size check"
Fixes: 9076c4e289d "nir: update opcode definitions for different bit sizes"
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Tested-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>