f2fs: introduce __try_update_largest_extent

This patch adds a new helper __try_update_largest_extent for cleanup.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index c9d1cfd..a38ee9b 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -351,8 +351,7 @@
 	}
 
 	if (en) {
-		if (en->ei.len > et->largest.len)
-			et->largest = en->ei;
+		__try_update_largest_extent(et, en);
 		et->cached_en = en;
 	}
 	return en;
@@ -389,8 +388,7 @@
 	if (!en)
 		return NULL;
 
-	if (en->ei.len > et->largest.len)
-		et->largest = en->ei;
+	__try_update_largest_extent(et, en);
 	et->cached_en = en;
 	return en;
 }
@@ -476,12 +474,10 @@
 				: NULL;
 		}
 
-		if (parts) {
-			if (en->ei.len > et->largest.len)
-				et->largest = en->ei;
-		} else {
+		if (parts)
+			__try_update_largest_extent(et, en);
+		else
 			__detach_extent_node(sbi, et, en);
-		}
 
 		/*
 		 * if original extent is split into zero or two parts, extent