ice: Check VF VSI Pointer Value in ice_vc_add_fdir_fltr()

In the Linux kernel, the following vulnerability has been resolved: ice: Check VF VSI Pointer Value in ice_vc_add_fdir_fltr() As mentioned in the commit baeb705fd6a7 ("ice: always check VF VSI pointer values"), we need to perform a null pointer check on the return value of ice_get_vf_vsi() before using it.