xen/blkfront: remove redundant flush_op
xen/blkfront: remove redundant flush_op

flush_op is unambiguously defined by feature_flush:
    REQ_FUA | REQ_FLUSH -> BLKIF_OP_WRITE_BARRIER
    REQ_FLUSH -> BLKIF_OP_FLUSH_DISKCACHE
    0 -> 0
and thus can be removed. This is just a cleanup.

The patch was suggested by Boris Ostrovsky.

Signed-off-by: Vitaly Kuznetsov <282517a3cdaae14e79e6d52f012bddb9ec2b7f0e@redhat.com>
Reviewed-by: Boris Ostrovsky <b41c17b861974b03cec38e3ec2992769b9bfae55@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs