ir3/merge_regs: Set wrmask for pcopy destinations

This was wrong, and with spilling we can now create vector phi's in rare
circumstances.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12033>

src/freedreno/ir3/ir3_merge_regs.c

@@ -429,7 +429,8 @@ create_parallel_copy(struct ir3_block *block)
       for (j = 0; j < phi_count; j++) {
          struct ir3_register *reg = __ssa_dst(pcopy);
          reg->flags |= src[j]->flags & (IR3_REG_HALF | IR3_REG_ARRAY);
-         reg->size = reg_elems(src[j]);
+         reg->size = src[j]->size;
+         reg->wrmask = src[j]->wrmask;
       }
 
       for (j = 0; j < phi_count; j++) {