s390/mm: Fix storage key clearing for guest huge pages

The function __storage_key_init_range() expects the end address to be
the first byte outside the range to be initialized. I.e. end - start
should be the size of the area to be initialized.

The current code works because __storage_key_init_range() will still loop
over every page in the range, but it is slower than using sske_frame().

Fixes: 964c2c0 ("s390/mm: Clear huge page storage keys on enable_skey")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20240416114220.28489-2-imbrenda@linux.ibm.com
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

Author: Claudio Imbrenda

arch/s390/mm/gmap.c

@@ -2661,7 +2661,7 @@ static int __s390_enable_skey_hugetlb(pte_t *pte, unsigned long addr,
 		return 0;
 
 	start = pmd_val(*pmd) & HPAGE_MASK;
-	end = start + HPAGE_SIZE - 1;
+	end = start + HPAGE_SIZE;
 	__storage_key_init_range(start, end);
 	set_bit(PG_arch_1, &page->flags);
 	cond_resched();