Update a stripe extent in case of an already existing logical address,
but with different physical addresses and/or device id instead of
bailing out with EEXIST.

This can happen i.e. in case of a device replace operation, where data
extents get rewritten to a new disk.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>