net: dsa: mt7530: set interrupt register only for MT7530

Setting this register related to interrupts is only needed for the MT7530
switch. Make an exclusive check to ensure this.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Acked-by: Daniel Golle <daniel@makrotopia.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>