Bump PicoRV32 version.

diff --git a/litex/soc/cores/cpu/picorv32/verilog b/litex/soc/cores/cpu/picorv32/verilog
index e630bedda4f16d5f061f93879177a2d6b2a66d29..a9e0ea54cffa162cfe901ff8d30d8877a18c6d8e 160000 (submodule)
--- a/litex/soc/cores/cpu/picorv32/verilog
+++ b/litex/soc/cores/cpu/picorv32/verilog
@@ -1 +1 @@
-Subproject commit e630bedda4f16d5f061f93879177a2d6b2a66d29
+Subproject commit a9e0ea54cffa162cfe901ff8d30d8877a18c6d8e