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 <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Vignesh Raghavendra <[e-mail]>
Cc: "Jochen Schäuble" <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/devices/phram.c

···
 // SPDX-License-Identifier: GPL-2.0-only
-/**
+/*
  * Copyright (c) ????		Jochen Schäuble <[e-mail]>
  * Copyright (c) 2003-2004	Joern Engel <[e-mail]>
  *