include/scsi/osd_protocol.h: remove unnecessary __constant

__constant_cpu_to_be16 converted to cpu_to_be16

This patch fixes checkpatch warnings:

"WARNING: __constant_cpu_to_be16 should be cpu_to_be16"

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Ack-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>