xfs: pass objects to the xrep_ibt_walk_rmap tracepoint

Pass the perag structure and the irec so that the decoding is only done
when tracing is actually enabled and the call sites look a lot neater,
and remove the pointless class indirection.

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