cores/usb: Add value init to decoded symbol in RX path (for sim only)

The actual value doesn't matter, but x propagations in this case screws
with simulation even if in actual hw, no matter what the initial value
is, it will "fix itself".

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

cores/usb/rtl/usb_rx_ll.v

@@ -62,7 +62,7 @@ module usb_rx_ll (
 	reg  [3:0] dec_sync_state_1;
 	reg  [3:0] dec_rep_state_1;
 
-	reg  [1:0] dec_sym_1;
+	reg  [1:0] dec_sym_1 = 2'b00;			/* Init is for simulation benefit only */
 	reg        dec_bit_1;
 	reg        dec_valid_1;
 	wire       dec_eop_1;