xfs: convert bp->b_bn references to xfs_buf_daddr()

xfs: convert bp->b_bn references to xfs_buf_daddr()

Source kernel commit: 9343ee76909e3f6466d85c9ebb0e343cdf54de71

Stop directly referencing b_bn in code outside the buffer cache, as
b_bn is supposed to be used only as an internal cache index.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>