When a zone (usually DMA) has no active pages, pages_scanned (which
triggers all_unreclaimable) is only incremented when scanning the active
list. 

Make sure it's incremented for scanned cache entries too.
Tested-by: Terje Fåberg <terje_fb@yahoo.no>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>