linux-user: remove duplicate break in syscall

likely introduced in 3532fa7402

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

@@ -3134,7 +3134,6 @@ set_timeout:
         case TARGET_SO_RCVLOWAT:
 		optname = SO_RCVLOWAT;
 		break;
-            break;
         default:
             goto unimplemented;
         }