nir: Avoid an extra NIR op in integer divide lowering.

NIR bools are ~0 for true, so ((unsigned)a >> 31) != 0 -> ((int)a >> 31).

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/nir/nir_lower_idiv.c

@@ -101,8 +101,7 @@ convert_instr(nir_builder *bld, nir_alu_instr *alu)
    if (is_signed)  {
       /* fix the sign: */
       r = nir_ixor(bld, numer, denom);
-      r = nir_ushr(bld, r, nir_imm_int(bld, 31));
-      r = nir_i2b(bld, r);
+      r = nir_ishr(bld, r, nir_imm_int(bld, 31));
       b = nir_ineg(bld, q);
       q = nir_bcsel(bld, r, b, q);
    }