mm/compaction.c: delete duplicated word

Drop the repeated word "a".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Link: http://lkml.kernel.org/r/20200801173822.14973-2-rdunlap@infradead.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/compaction.c

@@ -1477,7 +1477,7 @@ static void isolate_freepages(struct compact_control *cc)
 	 * this pfn aligned down to the pageblock boundary, because we do
 	 * block_start_pfn -= pageblock_nr_pages in the for loop.
 	 * For ending point, take care when isolating in last pageblock of a
-	 * a zone which ends in the middle of a pageblock.
+	 * zone which ends in the middle of a pageblock.
 	 * The low boundary is the end of the pageblock the migration scanner
 	 * is using.
 	 */