iavf: return errno code instead of status code

The iavf_parse_cls_flower function returns an integer error code, and
not an iavf_status enumeration.

Fix the function to use the standard errno value EINVAL as its return
instead of using IAVF_ERR_CONFIG.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>