xfs: refactor xlog_recover_buffer_pass1

Split out a xlog_add_buffer_cancelled helper which does the low-level
manipulation of the buffer cancelation table, and in that helper call
xlog_find_buffer_cancelled instead of open coding it.

Signed-off-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>