mm/page_isolation.c: remove redundant pfn_valid_within() in __first_valid_page()

pfn_valid_within() calls pfn_valid() when CONFIG_HOLES_IN_ZONE making it
redundant for both definitions (w/wo CONFIG_MEMORY_HOTPLUG) of the helper
pfn_to_online_page() which either calls pfn_valid() or pfn_valid_within().
pfn_valid_within() being 1 when !CONFIG_HOLES_IN_ZONE is irrelevant
either way.  This does not change functionality.

Link: http://lkml.kernel.org/r/1553141595-26907-1-git-send-email-anshuman.khandual@arm.comSigned-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_isolation.c

@@ -151,8 +151,6 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
 	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
 
-		if (!pfn_valid_within(pfn + i))
-			continue;
 		page = pfn_to_online_page(pfn + i);
 		if (!page)
 			continue;