kvm: selftests: dirty_log_test: always use -t

There's no reason not to always test the topmost physical
addresses, and if the user wants to try lower addresses
then '-p' (used to be '-o before this patch) can be used.
Let's remove the '-t' option and just always do what it did.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>