fix regression from commit 244f1441:

    $ make subdir-arm-softmmu
    make[1]: *** No rule to make target 'tci.o', needed by 'qemu-system-arm'.  Stop.
    Makefile:328: recipe for target 'subdir-arm-softmmu' failed
    make: *** [subdir-arm-softmmu] Error 2

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20170620163009.21764-1-f4bug@amsat.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>