f2fs: introduce f2fs_change_bit to simplify the change bit logic

Introduce f2fs_change_bit to simplify the change bit logic in
function set_to_next_nat{sit}.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 2495bec..6723ccc 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -657,10 +657,7 @@
 {
 	unsigned int block_off = SIT_BLOCK_OFFSET(start);
 
-	if (f2fs_test_bit(block_off, sit_i->sit_bitmap))
-		f2fs_clear_bit(block_off, sit_i->sit_bitmap);
-	else
-		f2fs_set_bit(block_off, sit_i->sit_bitmap);
+	f2fs_change_bit(block_off, sit_i->sit_bitmap);
 }
 
 static inline unsigned long long get_mtime(struct f2fs_sb_info *sbi)