mm: fixup unused variable warnings

mm: fixup unused variable warnings

Unfortunately fb_defio being enabled by nommu devices seems enormously
ingrained in the kernel to the point that it's not feasible to address
that in this series, so we use an ifdef to workaround.

However this workaround unfortunately missed some unused variables -
correct this.

This has been tested locally with W=1 and confirmed to resolve the issue.

Link: https://lkml.kernel.org/r/d4018405-2762-4385-a816-e54cc23839ac@lucifer.local
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Jaya Kumar <jayakumar.lkml@gmail.com>
Cc: Kajtar Zsolt <soci@c64.rulez.org>
Cc: Maíra Canal <mcanal@igalia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>