vfio/pci: fix a couple of spelling mistakes

There are several spelling mistakes, as follows:
thru ==> through
presense ==> presence

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210326083528.1329-4-thunder.leizhen@huawei.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>