Fixes the issues with non BCM58XX chips in the b53 driver
failing, when the irq is not specified in the device tree.

Removed the check for BCM58XX in b53_srab_prepare_irq(),
so the 'port->irq' will be set to '-EXIO' if the irq is not
specified in the device tree.

Fixes: 16994374 ("net: dsa: b53: Make SRAB driver manage port interrupts")
Fixes: b2ddc48a ("net: dsa: b53: Do not fail when IRQ are not initialized")
Signed-off-by: Arun Parameswaran <arun.parameswaran@broadcom.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>