s390/mm: Use pgprot_val() instead of open coding

Use pgprot_val() to get the page protection value, instead of accessing the
structure member directly. The type of pgprot_t is supposed to be hidden
from all users so that it can be changed; e.g. for STRICT_MM_TYPECHECKS.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: hcahca

arch/s390/mm/init.c

@@ -285,7 +285,7 @@ int arch_add_memory(int nid, u64 start, u64 size,
 	unsigned long size_pages = PFN_DOWN(size);
 	int rc;
 
-	if (WARN_ON_ONCE(params->pgprot.pgprot != PAGE_KERNEL.pgprot))
+	if (WARN_ON_ONCE(pgprot_val(params->pgprot) != pgprot_val(PAGE_KERNEL)))
 		return -EINVAL;
 
 	VM_BUG_ON(!mhp_range_allowed(start, size, true));