xfs: add helper for verifying checksums on xfs_bufs

Many/most callers of xfs_verify_cksum() pass bp->b_addr and
BBTOB(bp->b_length) as the first 2 args.  Add a helper
which can just accept the bp and the crc offset, and work
it out on its own, for brevity.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_linux.h

@@ -119,6 +119,7 @@ typedef __uint64_t __psunsigned_t;
 #include "xfs_iops.h"
 #include "xfs_aops.h"
 #include "xfs_super.h"
+#include "xfs_cksum.h"
 #include "xfs_buf.h"
 #include "xfs_message.h"