lightnvm: Avoid validation of default op value

Fixes: 38401d231de65 ("lightnvm: set target over-provision on create ioctl")
Signed-off-by: Heiner Litz <hlitz@ucsc.edu>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>