nvme-core: use nvme_is_io_ctrl() for I/O controller check

Replace the current I/O controller check in
nvme_init_non_mdts_limits() with the helper nvme_is_io_ctrl()
function to maintain consistency with similar checks in other
parts of the code and improve code readability.

Signed-off-by: Martin George <marting@netapp.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>