nvmet: Use enum definitions instead of hardcoded values

Change the definition of the inline functions nvmet_cc_en(),
nvmet_cc_css(), nvmet_cc_mps(), nvmet_cc_ams(), nvmet_cc_shn(),
nvmet_cc_iosqes(), and nvmet_cc_iocqes() to use the enum difinitions in
include/linux/nvme.h instead of hardcoded values.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>