xfs: remove xfs_alloc_arg firstblock field

The xfs_alloc_arg.firstblock field is used to control the starting
agno for an allocation. The structure already carries a pointer to
the transaction, which carries the current firstblock value.

Remove the field and access ->t_firstblock directly in the
allocation code.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_trace.h

@@ -1590,7 +1590,7 @@ DECLARE_EVENT_CLASS(xfs_alloc_class,
 		__entry->wasfromfl = args->wasfromfl;
 		__entry->resv = args->resv;
 		__entry->datatype = args->datatype;
-		__entry->firstblock = args->firstblock;
+		__entry->firstblock = args->tp->t_firstblock;
 	),
 	TP_printk("dev %d:%d agno %u agbno %u minlen %u maxlen %u mod %u "
 		  "prod %u minleft %u total %u alignment %u minalignslop %u "