octeontx2-pf: cn10k: Fix error return code in otx2_set_flowkey_cfg()

If otx2_mbox_get_rsp() fails, otx2_set_flowkey_cfg() need return an
error code.

Fixes: e7938365

 ("octeontx2-pf: Fix algorithm index in MCAM rules with RSS action")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>