s390/mm: correct allocate_pgste proc_handler callback

Since proc_dointvec does not perform value range control,
proc_dointvec_minmax should be used to limit value range, which is
clearly intended here, as the internal representation of the value:

unsigned int alloc_pgste:1;

In fact it currently works, since we have

      mm->context.alloc_pgste = page_table_allocate_pgste || ...

... since commit 23fefe11 ("s390/kvm: avoid global config of vm.alloc_pgste=1")

Before that it was

       mm->context.alloc_pgste = page_table_allocate_pgste;

which was broken. That was introduced with commit 0b46e0a3 ("s390/kvm:
remove delayed reallocation of page tables for KVM").

Fixes: 0b46e0a3 ("s390/kvm: remove delayed reallocation of page tables for KVM")
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/pgalloc.c

@@ -28,7 +28,7 @@ static struct ctl_table page_table_sysctl[] = {
 		.data		= &page_table_allocate_pgste,
 		.maxlen		= sizeof(int),
 		.mode		= S_IRUGO | S_IWUSR,
-		.proc_handler	= proc_dointvec,
+		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &page_table_allocate_pgste_min,
 		.extra2		= &page_table_allocate_pgste_max,
 	},