Fix miss value fencei instrucition in branch list

In the previous implementation, fencei was treated as a branch
instruction, but it was assigned a missing value in the new branch list.
As a result, emulator fails to pass Zifencei test.

Close: #98

Author: qwe661234

src/decode.h

@@ -62,7 +62,7 @@
     _(mret, 1)                             \
     /* RV32 Zifencei Standard Extension */ \
     IIF(RV32_HAS(Zifencei))(               \
-        _(fencei, 0)                       \
+        _(fencei, 1)                       \
     )                                      \
     /* RV32 Zicsr Standard Extension */    \
     IIF(RV32_HAS(Zicsr))(                  \

src/emulate.c

@@ -616,10 +616,10 @@ RVOP(hret, {
 RVOP(mret, { rv->PC = rv->csr_mepc; })
 
 #if RV32_HAS(Zifencei) /* RV32 Zifencei Standard Extension */
-RVOP(fencei,
-     {
-         /* FIXME: fill real implementations */
-     })
+RVOP(fencei, {
+    rv->PC += ir->insn_len;
+    /* FIXME: fill real implementations */
+})
 #endif
 
 #if RV32_HAS(Zicsr) /* RV32 Zicsr Standard Extension */