KVM: selftests: Fix spelling mistake "probabalistic" -> "probabilistic"

There is a spelling mistake in some help text. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Message-Id: <20221201091354.1613652-1-colin.i.king@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>