powerpc/rtas: Replaced simple_strtoull() with kstrtoull()

The simple_strtoull() function is deprecated in some situation, since
it does not check for the range overflow, use kstrtoull() instead.

Signed-off-by: Chen Huang <chenhuang5@huawei.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210526092020.554341-1-chenhuang5@huawei.com

arch/powerpc/kernel/rtas-proc.c

@@ -259,7 +259,6 @@ __initcall(proc_rtas_init);
 static int parse_number(const char __user *p, size_t count, u64 *val)
 {
 	char buf[40];
-	char *end;
 
 	if (count > 39)
 		return -EINVAL;
@@ -269,11 +268,7 @@ static int parse_number(const char __user *p, size_t count, u64 *val)
 
 	buf[count] = 0;
 
-	*val = simple_strtoull(buf, &end, 10);
-	if (*end && *end != '\n')
-		return -EINVAL;
-
-	return 0;
+	return kstrtoull(buf, 10, val);
 }
 
 /* ****************************************************************** */