sfc: remove unused variable 'efx_default_channel_type'

drivers/net/ethernet/sfc/efx.c:116:38: warning:
 efx_default_channel_type defined but not used [-Wunused-const-variable=]

commit 83975485 ("sfc: move channel alloc/removal code")
left behind this, remove it.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 83975485 ("sfc: move channel alloc/removal code")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Martin Habets <mhabets@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>