Introduce a helper function xfs_buf_daddr() to extract the disk
address of the buffer from the struct xfs_buf. This will replace
direct accesses to bp->b_bn and bp->b_maps[0].bm_bn, as well as
the XFS_BUF_ADDR() macro.

This patch introduces the helper function and replaces all uses of
XFS_BUF_ADDR() as this is just a simple sed replacement.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>