target/unicore32/translate: Add missing fallthrough annotations

Looking at the way the code is formatted here (there is an empty line
after break statements, but none where the break is missing), and the
instruction set overview at https://en.wikipedia.org/wiki/Unicore

 the
fallthrough is very likely intended here. So add a fallthrough comment
to make the it compilable with -Werror=implicit-fallthrough.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201211152426.350966-3-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

target/unicore32/translate.c

@@ -1801,6 +1801,7 @@ static void disas_uc32_insn(CPUUniCore32State *env, DisasContext *s)
             do_misc(env, s, insn);
             break;
         }
+        /* fallthrough */
     case 0x1:
         if (((UCOP_OPCODES >> 2) == 2) && !UCOP_SET_S) {
             do_misc(env, s, insn);
@@ -1817,6 +1818,7 @@ static void disas_uc32_insn(CPUUniCore32State *env, DisasContext *s)
         if (UCOP_SET(8) || UCOP_SET(5)) {
             ILLEGAL;
         }
+        /* fallthrough */
     case 0x3:
         do_ldst_ir(env, s, insn);
         break;