ceph: osd_client: fix endianness bug in osd_req_encode_op()

(cherry picked from commit 065a68f9167e20f321a62d044cb2c3024393d455)

From Al Viro <viro@zeniv.linux.org.uk>

Al Viro noticed that we were using a non-cpu-encoded value in
a switch statement in osd_req_encode_op().  The result would
clearly not work correctly on a big-endian machine.

Signed-off-by: Alex Elder <elder@dreamhost.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>