fpga-pio: fixes for hardening

Signed-off-by: Sean Cross <sean@xobs.io>
diff --git a/verilog/rtl/fpga_pio b/verilog/rtl/fpga_pio
index 9ca929a..48e53f9 160000
--- a/verilog/rtl/fpga_pio
+++ b/verilog/rtl/fpga_pio
@@ -1 +1 @@
-Subproject commit 9ca929a930e46411fed482069a27c75905285b68
+Subproject commit 48e53f97a3d3f4eaa3de6a0c380b2826d2f5738e