mm: make use of str_true_false helper

The helper str_true_false() was introduced to return "true/false" string
literal.  We can simplify this format by str_true_false.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Hongbo Li <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Trond Myklebust <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Hongbo Li

mm/memory-tiers.c

@@ -921,8 +921,7 @@ bool numa_demotion_enabled = false;
 static ssize_t demotion_enabled_show(struct kobject *kobj,
 				     struct kobj_attribute *attr, char *buf)
 {
-	return sysfs_emit(buf, "%s\n",
-			  numa_demotion_enabled ? "true" : "false");
+	return sysfs_emit(buf, "%s\n", str_true_false(numa_demotion_enabled));
 }
 
 static ssize_t demotion_enabled_store(struct kobject *kobj,