ice: drop pf == NULL check in ice_pf_state_is_nominal()

The function has 3 callers, all except one explicitly require
pf != NULL. Add the corresponding check to the remaining caller,
and remove it from the ice_pf_state_is_nominal(). It makse the
fun function a one-liner.

Signed-off-by: Yury Norov <ynorov@nvidia.com>
Reviewed-by: Sergey Temerkhanov <sergey.temerkhanov@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>