net: systemport: Omit superfluous error message in bcm_sysport_probe()

In the function bcm_sysport_probe(), when get irq failed, the function
platform_get_irq() logs an error message, so remove redundant message
here.

Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>