quota: use lockdep_assert_held_write in dquot_load_quota_sb

Use lockdep_assert_held_write to assert and self-document the locking
state in dquot_load_quota_sb instead of hand-crafting it with a trylock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230802115439.2145212-2-hch@lst.de>