pan/bi: Let !b2b imply branch_cond

Like the blob. Probably doesn't matter.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4505>

src/panfrost/bifrost/bi_pack.c

@@ -49,6 +49,8 @@ bi_pack_header(bi_clause *clause, bi_clause *next, bool is_fragment)
                 .next_clause_type = next ? next->clause_type : 0,
         };
 
+        header.branch_cond |= header.back_to_back;
+
         uint64_t u = 0;
         memcpy(&u, &header, sizeof(header));
         return u;