libceph: just have osd_req_op_init() return a pointer

The caller can just ignore the return. No need for this wrapper that
just casts the other function to void.

[ idryomov: argument alignment ]

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>