nvme: move passthrough logging attribute to head

The namespace does not have attributes, but the head does. Move the new
logging attribute to that structure instead of dereferencing the wrong
type.

And while we're here, fix the reverse-tree coding style.

Fixes: 9f079dda ("nvme: allow passthru cmd error logging")
Reported-by: Tasmiya Nalatwad <tasmiya@linux.vnet.ibm.com>
Tested-by: Tasmiya Nalatwad <tasmiya@linux.vnet.ibm.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Alan Adamson <alan.adamson@oracle.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>