mm/vmscan.c: clean code by removing unnecessary assignment

mm/vmscan.c: clean code by removing unnecessary assignment

Previously 0 was assigned to variable 'lruvec_size', but the variable was
never read later.  So the assignment can be removed.

Fixes: f87bccde6a7d ("mm/vmscan: remove unused lru_pages argument")
Change-Id: Iddd0982d271ee9ab9387195b87a4f608850cadc7
Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: http://lkml.kernel.org/r/20200229214022.11853-1-mateusznosek0@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[backport of the commit e072bff60a29c82b1536d78c412f009d1a1de4cf from mainline]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>