ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()

ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()

If we punch a hole on a reflink such that following conditions are met:

1. start offset is on a cluster boundary
2. end offset is not on a cluster boundary
3. (end offset is somewhere in another extent) or
   (hole range > MAX_CONTIG_BYTES(1MB)),

we dont COW the first cluster starting at the start offset. But in this
case, we were wrongly passing this cluster to
ocfs2_zero_range_for_truncate() to zero out. This will modify the cluster
in place and zero it in the source too.

Fix this by skipping this cluster in such a scenario.

Orabug: 24516161

Reported-by: Saar Maoz <saar.maoz@oracle.com>
Signed-off-by: Ashish Samant <ashish.samant@oracle.com>
Reviewed-by: Srinivas Eeda <srinivas.eeda@oracle.com>