btrfs: fix incorrect key offset in error message in check_dev_extent_item()

Fix the error message in check_dev_extent_item(), when an overlapping
stripe is encountered. For dev extents, objectid is the disk number and
offset the physical address, so prev_key->objectid should actually be
prev_key->offset.

(I can't take any credit for this one - this was discovered by Chris and
his friend Claude.)

Reported-by: Chris Mason <clm@fb.com>
Fixes: 008e251 ("btrfs: tree-checker: add dev extent item checks")
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Mark Harmstone <mark@harmstone.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: maharmstone

fs/btrfs/tree-checker.c

@@ -1921,7 +1921,7 @@ static int check_dev_extent_item(const struct extent_buffer *leaf,
 		if (unlikely(prev_key->offset + prev_len > key->offset)) {
 			generic_err(leaf, slot,
 		"dev extent overlap, prev offset %llu len %llu current offset %llu",
-				    prev_key->objectid, prev_len, key->offset);
+				    prev_key->offset, prev_len, key->offset);
 			return -EUCLEAN;
 		}
 	}