mm/sparse.c: remove NULL check in clear_hwpoisoned_pages()

There is no possibility for memmap to be NULL in the current codebase.

This check was added in commit 95a4774d ("memory-hotplug: update
mce_bad_pages when removing the memory") where memmap was originally
inited to NULL, and only conditionally given a value.

The code that could have passed a NULL has been removed by commit
ba72b4c8 ("mm/sparsemem: support sub-section hotplug"), so there is no
longer a possibility that memmap can be NULL.

Link: http://lkml.kernel.org/r/20190829035151.20975-1-alastair@d-silva.orgSigned-off-by: Alastair D'Silva <alastair@d-silva.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/sparse.c

@@ -896,9 +896,6 @@ static void clear_hwpoisoned_pages(struct page *memmap, int nr_pages)
 {
 	int i;
 
-	if (!memmap)
-		return;
-
 	/*
 	 * A further optimization is to have per section refcounted
 	 * num_poisoned_pages.  But that would need more space per memmap, so