Fix a TCG crash due to attempting an atomic increment
operation without having set up the address first.
This is a similar case to that dealt with in commit
e84fcd7f, and we fix it in the same way.

Fixes: https://bugs.launchpad.net/qemu/+bug/1807675


Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20190328104750.25046-1-peter.maydell@linaro.org