lightnvm: pblk: enable line minor version detection

When recovering a line, an extra check was added when debugging was
active, such that minor version where also checked. Unfortunately,
this used the ifdef NVM_DEBUG, which is not correct.

Instead use the proper DEBUG def, and now that it compiles, also fix
the variable.

Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Fixes: d0ab0b1a ("lightnvm: pblk: check data lines version on recovery")
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>