xfs: refactor xfs_qm_scall_setqlim

Now that we can pass around quota resource and limit structures, clean
up the open-coded field setting in xfs_qm_scall_setqlim.

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