microsoft/compiler: Set num_components to 4 when updating pos write instructions

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20614>

src/microsoft/compiler/dxil_nir.c

@@ -2031,6 +2031,7 @@ update_writes(struct nir_builder *b, nir_instr *instr, void *_state)
       if (!channels[i])
          channels[i] = nir_imm_intN_t(b, 0, src->bit_size);
 
+   intr->num_components = 4;
    nir_instr_rewrite_src_ssa(instr, &intr->src[0], nir_vec(b, channels, 4));
    nir_intrinsic_set_component(intr, 0);
    nir_intrinsic_set_write_mask(intr, 0xf);