s390/mm: Fix phys_to_folio() usage in do_secure_storage_access()

In case of a Secure-Storage-Access exception the effective aka virtual
address which caused the exception is contained within the TEID.

do_secure_storage_access() incorrectly uses phys_to_folio() instead of
virt_to_folio() to translate the virtual address to the corresponding
folio.

Fix this by using virt_to_folio() instead of phys_to_folio().

Fixes: 084ea4d611a3 ("s390/mm: add (non)secure page access exceptions handlers")
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>