pan/va: fix WMASK packing

WMASK's subgroup argument wasn't being encoded so we'd always
end up with a WMASK.subgroup2.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32710>

src/panfrost/compiler/valhall/va_pack.c

@@ -531,6 +531,10 @@ va_pack_alu(const bi_instr *I)
       hex |= ((uint64_t)I->texture_index) << 20;
       break;
 
+   case BI_OPCODE_WMASK:
+      hex |= ((uint64_t)I->subgroup) << 36;
+      break;
+
    case BI_OPCODE_ZS_EMIT:
       if (I->stencil)
          hex |= (1 << 24);