net-next: mediatek: remove superfluous free_irq() call

Commit 80673029 ("net-next: mediatek: add support for IRQ grouping")
adds handling for irq 1 and 2 to the uninit function but did not remove
irq 0 which is not used since irq grouping was introduced. Fix this by
removing the superfluous call to free_irq().

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: John Crispin <john@phrozen.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>