linux-user: Add missing 'break' in i386 get_thread_area syscall

The i386 code for the get_thread_area syscall was missing a
'break' which meant it would have fallen through into the
implementation of the following syscall; add it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

@@ -8572,6 +8572,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
     case TARGET_NR_get_thread_area:
 #if defined(TARGET_I386) && defined(TARGET_ABI32)
         ret = do_get_thread_area(cpu_env, arg1);
+        break;
 #elif defined(TARGET_M68K)
         {
             TaskState *ts = ((CPUArchState *)cpu_env)->opaque;