xfs: refactor reflink functions to use xfs_trans_alloc_inode

The two remaining callers of xfs_trans_reserve_quota_nblks are in the
reflink code.  These conversions aren't as uniform as the previous
conversions, so call that out in a separate patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>