Commit d0ed8076 converted the PCI config access to the memory
API, but also inadvertantly changed it to accept unaligned writes,
and corrupt the index register in the process.  This causes a regression
booting NetBSD.

Fix by ignoring unaligned or non-dword writes.

https://bugs.launchpad.net/qemu/+bug/897771Reported-by: NAndreas Gustafsson <gson@gson.org>
Signed-off-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>