nvme/pci: Fix write and poll queue types

nvme/pci: Fix write and poll queue types

BugLink: https://bugs.launchpad.net/bugs/1860125
[ Upstream commit 3f68baf706ec68c4120867c25bc439c845fe3e17 ]

The number of poll or write queues should never be negative. Use unsigned
types so that it's not possible to break have the driver not allocate
any queues.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>