Persian is not just the language of Iran.. it is the language of all countries of GREATER IRAN (which includes Western parts of Pakistan, Tajikistan, Afghanistan).. Deep Urdu is quite similar to Persian... If you read deep Urdu poetry written by great Urdu poets like Iqbal etc, it is in Persian. And Pakistan holding second largest Iranic population after Iran (Pashtuns, Balochis and Farsiwans)... having our National Anthem and country's name root in Persian isn't out of place.
The official language of Punjab and Sindh was also Persian before partition. Therefore, having our national anthem in Persian and linking ourselves with Persian culture is still NOT OF PLACE. Unlike your country's name and national anthem which was first sung to welcome George V on his visit to India.. references to Sindh and naming your country on something which isn't part of India anymore..