mtd: devices: phram: File headers are not good candidates for kernel-doc

Fixes the following W=1 kernel build warning(s):

 drivers/mtd/devices/phram.c:19: warning: Function parameter or member 'fmt' not described in 'pr_fmt'

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: "Jochen Schäuble" <psionic@psionic.de>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201109182206.3037326-3-lee.jones@linaro.org

drivers/mtd/devices/phram.c

 // SPDX-License-Identifier: GPL-2.0-only
-/**
+/*
  * Copyright (c) ????		Jochen Schäuble <psionic@psionic.de>
  * Copyright (c) 2003-2004	Joern Engel <joern@wh.fh-wedel.de>
  *