vkd3d-shader/hlsl: Use bool type for new_cond in lower_conditional_block_discard_nz().
Fixes the assertion error
sm4_generate_vsir_instr_expr Failed assertion: dst_type->e.numeric.type == HLSL_TYPE_BOOL,
which occurs when compiling the following ps_4_0 shader:
uniform float4 x;
uniform bool b;
float4 main() : SV_Target
{
if (!b)
clip(x.x);
else
clip(x.y);
return x;
}