ahci: Fix compiling warnings under 64bit platforms

When compling under 64bit platforms, there are lots of warnings,
like:

drivers/block/ahci.c:114:18: warning: cast to pointer from integer
 of different size [-Wint-to-pointer-cast]
  u8 *port_mmio = (u8 *)probe_ent->port[port].port_mmio;
                  ^
drivers/block/ahci.c: In function ?.hci_host_init?.
drivers/block/ahci.c:218:49: warning: cast from pointer to integer
 of different size [-Wpointer-to-int-cast]
   probe_ent->port[i].port_mmio = ahci_port_base((u32) mmio, i);

......

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Tang Yuantian <Yuantian.Tang@freescale.com>