net: designware: Fix build warnings

When building dm version of designware eth driver on a platform
with 64-bit phys_addr_t, it reports the following warnings:

  drivers/net/designware.c: In function 'designware_eth_probe':
  drivers/net/designware.c:599:2:
    warning: format '%lx' expects argument of type 'long unsigned int',
    but argument 3 has type 'phys_addr_t' [-Wformat]
  drivers/net/designware.c:600:21:
    warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
  drivers/net/designware.c:601:21:
    warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

This commit fixes the build warnings.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>