CMA: make putback_lru_pages() call conditional

As per documentation and other places calling putback_lru_pages(),
putback_lru_pages() is called on error only.  Make the CMA code behave
consistently.

[akpm@linux-foundation.org: remove a test-n-branch in the wrapup code]
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -5806,9 +5806,11 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
 				    0, false, MIGRATE_SYNC,
 				    MR_CMA);
 	}
-
-	putback_movable_pages(&cc->migratepages);
-	return ret > 0 ? 0 : ret;
+	if (ret < 0) {
+		putback_movable_pages(&cc->migratepages);
+		return ret;
+	}
+	return 0;
 }
 
 /**