lightnvm: fix "warning: ‘ret’ may be used uninitialized"

This fixes the following warnings:
drivers/lightnvm/sysblk.c:125:9: warning: ‘ret’ may be used
uninitialized in this function

drivers/lightnvm/sysblk.c:275:15: warning: ‘ret’ may be used
uninitialized in this function

In both cases, ret is only set from within a loop that may not be entered.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>