btrfs: check return value of btrfs_partially_delete_raid_extent()

btrfs: check return value of btrfs_partially_delete_raid_extent()

btrfs_partially_delete_raid_extent() returns an error code (e.g.
-ENOMEM from kzalloc(), or errors from btrfs_del_item/btrfs_insert_item()),
but all three call sites in btrfs_delete_raid_extent() discard the
return value, silently losing errors and potentially leaving the stripe
tree in an inconsistent state.

Fix by capturing the return value into ret at all three call sites and
breaking out of the loop on error where appropriate.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: robbieko <robbieko@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>