cirrus: cs89x0: remove set but not used variable 'lp'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/cirrus/cs89x0.c: In function 'cs89x0_platform_probe':
drivers/net/ethernet/cirrus/cs89x0.c:1847:20: warning:
 variable 'lp' set but not used [-Wunused-but-set-variable]

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 6751edeb

 ("cirrus: cs89x0: Use managed interfaces")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>