[PATCH] configfs: Lock new directory inodes before removing on cleanup after failure

Once a new configfs directory is created by configfs_attach_item() or
configfs_attach_group(), a failure in the remaining initialization steps leads
to removing a directory which inode the VFS may have already accessed.

This commit adds the necessary inode locking to safely remove configfs
directories while cleaning up after a failure. As an advantage, the locking
rules of populate_groups() and detach_groups() become the same: the caller must
have the group's inode mutex locked.

Signed-off-by: Louis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>