xfs: don't use xfs_trans_reserve in xfs_trans_roll

xfs: don't use xfs_trans_reserve in xfs_trans_roll

xfs_trans_roll uses xfs_trans_reserve to basically just call into
xfs_log_regrant while bypassing the reset of xfs_trans_reserve.

Open code the call to xfs_log_regrant in xfs_trans_roll and simplify
xfs_trans_reserve now that it never regrants and always asks for a log
reservation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>