Btrfs: fix btrfs acl #ifdef checks

The btrfs acl code was #ifdefing for a define
that didn't exist.  This correctly matches it
to the values used by the Kconfig file.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e0a6432..3fbbf07 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -344,7 +344,7 @@
 	sb->s_export_op = &btrfs_export_ops;
 	sb->s_xattr = btrfs_xattr_handlers;
 	sb->s_time_gran = 1;
-#ifdef CONFIG_BTRFS_POSIX_ACL
+#ifdef CONFIG_BTRFS_FS_POSIX_ACL
 	sb->s_flags |= MS_POSIXACL;
 #endif