f2fs: use inner macro and function to clean up codes

In this patch we use below inner macro and function to clean up codes.
1. ADDRS_PER_PAGE
2. SM_I
3. f2fs_readonly

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 8f96d93..870fe19 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -615,7 +615,7 @@
 	 * Previous and new state of filesystem is RO,
 	 * so skip checking GC and FLUSH_MERGE conditions.
 	 */
-	if ((sb->s_flags & MS_RDONLY) && (*flags & MS_RDONLY))
+	if (f2fs_readonly(sb) && (*flags & MS_RDONLY))
 		goto skip;
 
 	/*
@@ -642,8 +642,7 @@
 	 */
 	if ((*flags & MS_RDONLY) || !test_opt(sbi, FLUSH_MERGE)) {
 		destroy_flush_cmd_control(sbi);
-	} else if (test_opt(sbi, FLUSH_MERGE) &&
-					!sbi->sm_info->cmd_control_info) {
+	} else if (test_opt(sbi, FLUSH_MERGE) && !SM_I(sbi)->cmd_control_info) {
 		err = create_flush_cmd_control(sbi);
 		if (err)
 			goto restore_gc;
@@ -1082,7 +1081,7 @@
 	 * If filesystem is not mounted as read-only then
 	 * do start the gc_thread.
 	 */
-	if (!(sb->s_flags & MS_RDONLY)) {
+	if (!f2fs_readonly(sb)) {
 		/* After POR, we can run background GC thread.*/
 		err = start_gc_thread(sbi);
 		if (err)