KVM: selftests: aarch64: Fix check of dirty log PT write

The dirty log checks are mistakenly testing the first page in the page
table (PT) memory region instead of the page holding the test data
page PTE.  This wasn't an issue before commit 406504c7 ("KVM:
arm64: Fix S1PTW handling on RO memslots") as all PT pages (including
the first page) were treated as writes.

Fix the page_fault_test dirty logging tests by checking for the right
page: the one for the PTE of the data test page.

Fixes: a4edf25b ("KVM: selftests: aarch64: Add dirty logging tests into page_fault_test")
Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230127214353.245671-4-ricarkol@google.com