mm: memory_hotplug: remove second __nr_to_section in register_page_bootmem_info_section()

In register_page_bootmem_info_section() we call __nr_to_section() in
order to get the mem_section struct at the beginning of the function.
Since we already got it, there is no need for a second call to
__nr_to_section().

Link: http://lkml.kernel.org/r/20171207102914.GA12396@techadventures.net
Signed-off-by: Oscar Salvador <osalvador@techadventures.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -184,7 +184,7 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)
 	for (i = 0; i < mapsize; i++, page++)
 		get_page_bootmem(section_nr, page, SECTION_INFO);
 
-	usemap = __nr_to_section(section_nr)->pageblock_flags;
+	usemap = ms->pageblock_flags;
 	page = virt_to_page(usemap);
 
 	mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;
@@ -207,7 +207,7 @@ static void register_page_bootmem_info_section(unsigned long start_pfn)
 
 	register_page_bootmem_memmap(section_nr, memmap, PAGES_PER_SECTION);
 
-	usemap = __nr_to_section(section_nr)->pageblock_flags;
+	usemap = ms->pageblock_flags;
 	page = virt_to_page(usemap);
 
 	mapsize = PAGE_ALIGN(usemap_size()) >> PAGE_SHIFT;