nilfs2: get rid of nilfs_mount_options structure

Only mount_opt member is used in the nilfs_mount_options structure,
and we can simplify it.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index f0ab826..6ea32d9 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -1019,11 +1019,11 @@
 	struct nilfs_sb_info *sbi = NILFS_SB(sb);
 	struct the_nilfs *nilfs = sbi->s_nilfs;
 	unsigned long old_sb_flags;
-	struct nilfs_mount_options old_opts;
+	unsigned long old_mount_opt;
 	int err;
 
 	old_sb_flags = sb->s_flags;
-	old_opts.mount_opt = sbi->s_mount_opt;
+	old_mount_opt = sbi->s_mount_opt;
 
 	if (!parse_options(data, sb, 1)) {
 		err = -EINVAL;
@@ -1092,7 +1092,7 @@
 
  restore_opts:
 	sb->s_flags = old_sb_flags;
-	sbi->s_mount_opt = old_opts.mount_opt;
+	sbi->s_mount_opt = old_mount_opt;
 	return err;
 }