mtd: rawnand: vf610_nfc: add initializer to avoid -Wmaybe-uninitialized

mtd: rawnand: vf610_nfc: add initializer to avoid -Wmaybe-uninitialized

This prepares to move CONFIG_OPTIMIZE_INLINING from x86 to a common
place.  We need to eliminate potential issues beforehand.

Kbuild test robot has never reported -Wmaybe-uninitialized warning for
this probably because vf610_nfc_run() is inlined by the x86 compiler's
inlining heuristic.

If CONFIG_OPTIMIZE_INLINING is enabled for a different architecture and
vf610_nfc_run() is not inlined, the following warning is reported:

  drivers/mtd/nand/raw/vf610_nfc.c: In function `vf610_nfc_cmd':
  drivers/mtd/nand/raw/vf610_nfc.c:455:3: warning: `offset' may be used uninitialized in this function [-Wmaybe-uninitialized]
     vf610_nfc_rd_from_sram(instr->ctx.data.buf.in + offset,
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
              nfc->regs + NFC_MAIN_AREA(0) + offset,
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
              trfr_sz, !nfc->data_access);
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~

Link: http://lkml.kernel.org/r/20190423034959.13525-6-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boris Brezillon <bbrezillon@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Stefan Agner <stefan@agner.ch>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>