nvme: avoid double dereference to convert le to cpu

Use le16_to_cpu instead of le16_to_cpup and le64_to_cpu instead of
le64_to_cpup. This will also align the code to nvme-core driver
convention.

Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>