net: ethernet: ti: cpsw: Push the request_irq function to the end of probe

Push the request_irq function to the end of probe so as
to ensure all the required fields are populated in the event
of an ISR getting executed right after requesting the irq.

Currently while loading the crash kernel a crash was seen as
soon as devm_request_threaded_irq was called. This was due to
n->poll being NULL which is called as part of net_rx_action
function.

Suggested-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>