lightnvm: invalid offset calculation for lba_shift

The ns->lba_shift assumes its value to be the logarithmic of the
LA size. A previous patch duplicated the lba_shift calculation into
lightnvm. It prematurely also subtracted a 512byte shift, which commonly
is applied per-command. The 512byte shift being subtracted twice led to
data loss when restoring the logical to physical mapping table from
device and when issuing I/O commands using rrpc.

Fix offset by removing the 512byte shift subtraction when calculating
lba_shift.

Fixes: b0b4e09c1ae7 "lightnvm: control life of nvm_dev in driver"
Reported-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/nvme/host/lightnvm.c

@@ -612,7 +612,7 @@ int nvme_nvm_register(struct nvme_ns *ns, char *disk_name, int node,
 
 	ret = nvm_register(dev);
 
-	ns->lba_shift = ilog2(dev->sec_size) - 9;
+	ns->lba_shift = ilog2(dev->sec_size);
 
 	if (sysfs_create_group(&dev->dev.kobj, attrs))
 		pr_warn("%s: failed to create sysfs group for identification\n",