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/f2fs.h b/fs/f2fs/f2fs.h
index 3608c13..60045a2 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1073,6 +1073,15 @@
 	return ret;
 }
 
+static inline void f2fs_change_bit(unsigned int nr, char *addr)
+{
+	int mask;
+
+	addr += (nr >> 3);
+	mask = 1 << (7 - (nr & 0x07));
+	*addr ^= mask;
+}
+
 /* used for f2fs_inode_info->flags */
 enum {
 	FI_NEW_INODE,		/* indicate newly allocated inode */