btrfs: update panic message when splitting ordered extent

During ordered extent splitting if we find a duplicated ordered extent
when attempting to insert the new ordered extent we panic but with a
message that has the "zoned:" prefix. This is because the splitting used
to be exclusive for zoned filesystems, but as of commit b73a6fd1
("btrfs: split partial dio bios before submit") it can also be done for
non zoned filesystems during direct IO writes. So remove the "zoned:"
prefix from the message and mention the split to make it more specific
and different from the panic message at insert_ordered_extent().

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>