xfs: rename the old_crc variable in xlog_recover_process

old_crc is a very misleading name.  Rename it to expected_crc as that
described the usage much better.

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