mfd: Represent correct filenames in file headers

The original author(s) probably copy/pasted these headers from the
existing public header files.
Signed-off-by: Laszlo Papp <lpapp@kde.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

include/linux/mfd/max77686-private.h

 /*
- * max77686.h - Voltage regulator driver for the Maxim 77686
+ * max77686-private.h - Voltage regulator driver for the Maxim 77686
  *
  *  Copyright (C) 2012 Samsung Electrnoics
  *  Chiwoong Byun <woong.byun@samsung.com>

include/linux/mfd/max8997-private.h

 /*
- * max8997.h - Voltage regulator driver for the Maxim 8997
+ * max8997-private.h - Voltage regulator driver for the Maxim 8997
  *
  *  Copyright (C) 2010 Samsung Electrnoics
  *  MyungJoo Ham <myungjoo.ham@samsung.com>

include/linux/mfd/max8998-private.h

 /*
- * max8998.h - Voltage regulator driver for the Maxim 8998
+ * max8998-private.h - Voltage regulator driver for the Maxim 8998
  *
  *  Copyright (C) 2009-2010 Samsung Electrnoics
  *  Kyungmin Park <kyungmin.park@samsung.com>