lightnvm: fix out-of-bounds write to array devices->info[]

There is an off-by-one array check that can lead to a out-of-bounds
write to devices->info[i].  Fix this by checking by using >= rather
than > for the size check. Also replace hard-coded array size limit
with ARRAY_SIZE on the array.

Addresses-Coverity: ("Out-of-bounds write")
Fixes: cd9e9808 ("lightnvm: Support for Open-Channel SSDs")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>