ceph: fix file open flags on ppc64

The file open flags (O_foo) are platform specific and should never go
out to an interface that is not local to the system.

Unfortunately these flags have leaked out onto the wire in the cephfs
implementation. That lead to bogus flags getting transmitted on ppc64.

This patch converts the kernel view of flags to the ceph view of file
open flags.

Fixes: 124e68e7 ("ceph: file operations")
Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>