hw/misc/arm_sysctl: Fix bad boundary check on mb clock accesses

Fix incorrect use of sizeof() rather than ARRAY_SIZE() to guard
accesses into the mb_clock[] array, which was allowing a malicious
guest to overwrite the end of the array.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Message-id: 1392647854-8067-2-git-send-email-peter.maydell@linaro.org
Cc: qemu-stable@nongnu.org
