net: ks8851: Delay requesting IRQ until opened

The ks8851 driver currently requests the IRQ before registering the
net_device.  Because the net_device name is used as IRQ name and is
still "eth%d" when the IRQ is requested, it's impossibe to tell IRQs
apart if multiple ks8851 chips are present.  Most other drivers delay
requesting the IRQ until the net_device is opened.  Do the same.

The driver doesn't enable interrupts on the chip before opening the
net_device and disables them when closing it, so there doesn't seem to
be a need to request the IRQ already on probe.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>