xfs: refactor xfs_trans_apply_dquot_deltas

Hoist the code that adjusts the incore quota reservation count
adjustments into a separate function, both to reduce the level of
indentation and also to reduce the amount of open-coded logic.

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