lightnvm: put block back to gc list on its reclaim fail

We delete a block from the gc list before reclaim it, so
put it back to the list on its reclaim fail, otherwise
this block will not get reclaimed and be programmable
in the future.

Signed-off-by: Wenwei Tao <ww.tao0320@gmail.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>