target/arm: Early exit after unallocated_encoding in disas_fp_int_conv

No sense in emitting code after the exception.
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
Tested-by: NAlex Bennée <alex.bennee@linaro.org>
Message-id: 20180512003217.9105-3-richard.henderson@linaro.org
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/arm/translate-a64.c

@@ -5780,7 +5780,7 @@ static void disas_fp_int_conv(DisasContext *s, uint32_t insn)
         default:
             /* all other sf/type/rmode combinations are invalid */
             unallocated_encoding(s);
-            break;
+            return;
         }
 
         if (!fp_access_check(s)) {