net/i40e: fix check of flow director programming status

net/i40e: fix check of flow director programming status

In i40e FDIR PMD code for checking programming status
function i40e_check_fdir_programming_status(), the initial value
of return value ret should be set to -1 not 0, because if DD bit of
I40E_RX_DESC_STATUS_DD is not write back, this function will return
0 to upper function, this give an error info to upper function, the
fact for this is it is time out for DD write back and it should return
-1.

Fixes: 05999aab4ca6 ("i40e: add or delete flow director")
Cc: stable@dpdk.org
Signed-off-by: Wei Zhao <wei.zhao1@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>