xfs: refactor xfs_trans_dqresv

Now that we've refactored the resource usage and limits into
per-resource structures, we can refactor some of the open-coded
reservation limit checking in xfs_trans_dqresv.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>