f2fs: add unlikely() macro for compiler more aggressively

This patch adds unlikely() macro into the most of codes.
The basic rule is to add that when:
- checking unusual errors,
- checking page mappings,
- and the other unlikely conditions.

Change log from v1:
 - Don't add unlikely for the NULL test and error test: advised by Andi Kleen.

Cc: Chao Yu <chao2.yu@samsung.com>
Cc: Andi Kleen <andi@firstfloor.org>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 2b47adc..5accc96 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -50,9 +50,9 @@
 
 	file_update_time(vma->vm_file);
 	lock_page(page);
-	if (page->mapping != inode->i_mapping ||
+	if (unlikely(page->mapping != inode->i_mapping ||
 			page_offset(page) > i_size_read(inode) ||
-			!PageUptodate(page)) {
+			!PageUptodate(page))) {
 		unlock_page(page);
 		err = -EFAULT;
 		goto out;
@@ -120,7 +120,7 @@
 		.for_reclaim = 0,
 	};
 
-	if (f2fs_readonly(inode->i_sb))
+	if (unlikely(f2fs_readonly(inode->i_sb)))
 		return 0;
 
 	trace_f2fs_sync_file_enter(inode);
@@ -241,7 +241,7 @@
 		return;
 
 	lock_page(page);
-	if (page->mapping != inode->i_mapping) {
+	if (unlikely(page->mapping != inode->i_mapping)) {
 		f2fs_put_page(page, 1);
 		return;
 	}
@@ -516,7 +516,6 @@
 		if (ret)
 			break;
 
-
 		if (pg_start == pg_end)
 			new_size = offset + len;
 		else if (index == pg_start && off_start)