ACPI: fix obsolete comment in custom_method.c

The comment describing the contents of the custom_method.c file is
obsolete, so update it.

[rjw: Subject and changelog]
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/custom_method.c

 /*
- * debugfs.c - ACPI debugfs interface to userspace.
+ * custom_method.c - debugfs interface for customizing ACPI control method
  */
 
 #include <linux/init.h>