ext4: Simplify the usage of clear_opt() and set_opt() macros

Change clear_opt() and set_opt() to take a superblock pointer instead
of a pointer to EXT4_SB(sb)->s_mount_opt.  This makes it easier for us
to support a second mount option field.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5b4d4e3..731b6f7 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2617,7 +2617,7 @@
 	ret = sb_issue_discard(sb, discard_block, count, GFP_NOFS, 0);
 	if (ret == -EOPNOTSUPP) {
 		ext4_warning(sb, "discard not supported, disabling");
-		clear_opt(EXT4_SB(sb)->s_mount_opt, DISCARD);
+		clear_opt(sb, DISCARD);
 	}
 	return ret;
 }