9p: re-enable mount time debug option

During reorganization, the mount time debug option was removed in favor
of module-load-time parameters.  However, the mount time option is still
a useful for feature during debug and for user-fault isolation when the
module is compiled into the kernel.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
index f6a0519..ba90437 100644
--- a/fs/9p/vfs_super.c
+++ b/fs/9p/vfs_super.c
@@ -217,7 +217,7 @@
 	struct v9fs_session_info *v9ses = mnt->mnt_sb->s_fs_info;
 
 	if (v9ses->debug != 0)
-		seq_printf(m, ",debug=%u", v9ses->debug);
+		seq_printf(m, ",debug=%x", v9ses->debug);
 	if (v9ses->port != V9FS_PORT)
 		seq_printf(m, ",port=%u", v9ses->port);
 	if (v9ses->maxdata != 9000)