target-arm/gdbstub64.c: remove useless 'break' statement. Clean up useless 'break' statement after 'return' statement. Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com> Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>