kvm-all: don't use stale dbg_data->cpu

kvm-all: don't use stale dbg_data->cpu

The changes to run_on_cpu and friends mean that all helpers are passed
the CPUState of vCPU they are running on. The conversion missed the
field in commit e0eeb4a21a3ca4b296220ce4449d8acef9de9049 which
introduced bugs.

Reported-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Tested-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20161010154625.14881-1-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>