KVM: s390: Do not set special large pages dirty

Special pages / folios should not be set dirty. This also applies to
large pages.

Add a missing check in gmap_clear_young_crste() to prevent setting the
large page dirty if it is a special page.

Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260623153331.233784-4-imbrenda@linux.ibm.com>