inode: clarify what's locked

In __wait_on_freeing_inode() we warn in case the inode_hash_lock is held
but the inode is unhashed. We then release the inode_lock. So using
"locked" as parameter name is confusing. Use is_inode_hash_locked as
parameter name instead.

Signed-off-by: Christian Brauner <brauner@kernel.org>