mm: fix compile error due to COMPACTION_HPAGE_ORDER

Fix compile error when COMPACTION_HPAGE_ORDER is assigned to
HUGETLB_PAGE_ORDER.  The correct way to check if this constant is defined
is to check for CONFIG_HUGETLBFS.
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nitin Gupta <nigupta@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: http://lkml.kernel.org/r/20200623064544.25766-1-nigupta@nvidia.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -62,7 +62,7 @@ static const int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
  */
 #if defined CONFIG_TRANSPARENT_HUGEPAGE
 #define COMPACTION_HPAGE_ORDER	HPAGE_PMD_ORDER
-#elif defined HUGETLB_PAGE_ORDER
+#elif defined CONFIG_HUGETLBFS
 #define COMPACTION_HPAGE_ORDER	HUGETLB_PAGE_ORDER
 #else
 #define COMPACTION_HPAGE_ORDER	(PMD_SHIFT - PAGE_SHIFT)