axi_dmac: request_arb: Add missing req_gen_{valid,ready} signal declaration

Make sure the req_gen_valid and req_gen_ready signals are declared before
they are used. Strictly speaking the current code is correct and synthesis
correctly, but declaring the signals make the intentions of the code more
explicit.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

library/axi_dmac/request_arb.v

@@ -200,6 +200,8 @@ wire src_pause;
 wire src_sync_id;
 wire src_sync_id_ret;
 
+wire req_gen_valid;
+wire req_gen_ready;
 wire req_dest_valid;
 wire req_dest_ready;
 wire req_dest_empty;