[examples/fpga] Fix memory interface

Logic driving instr_gnt/data_gnt violated Ibex memory protocol. It just
happened to work until a recent change.

Fixes #1500

Author: GregAC

examples/fpga/artya7/rtl/top_artya7.sv

@@ -111,17 +111,8 @@ module top_artya7 (
     .b_rdata_o (instr_rdata)
   );
 
-
-  // SRAM to Ibex
-  always_ff @(posedge clk_sys or negedge rst_sys_n) begin
-    if (!rst_sys_n) begin
-      instr_gnt    <= '0;
-      data_gnt     <= '0;
-    end else begin
-      instr_gnt    <= instr_req ;
-      data_gnt     <=  data_req ;
-    end
-  end
+  assign instr_gnt = instr_req;
+  assign data_gnt  = data_req;
 
   // Connect the LED output to the lower four bits of the most significant
   // byte