Use helper function zone_spans_pfn() to check whether pfn is within a
zone to simplify the code slightly.

Link: https://lkml.kernel.org/r/20210902121242.41607-5-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>