mm/memory.c: initialise mmu_notifier_range correctly

One of the paths in follow_pte_pmd() initialised the mmu_notifier_range
incorrectly.

Link: http://lkml.kernel.org/r/20190103002126.GM6310@bombadil.infradead.org


Fixes: ac46d4f3 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Tested-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>