driver: dwmmc: Fix pointer conversion warnings for hikey

Fix below compilation warings happening for hikey_defconfig

drivers/mmc/dw_mmc.c: In function ‘dwmci_set_idma_desc’:
drivers/mmc/dw_mmc.c:43:20: warning: cast from pointer to integer
of different size [-Wpointer-to-int-cast]
  desc->next_addr = (unsigned int)desc + sizeof(struct dwmci_idmac);
                    ^
drivers/mmc/dw_mmc.c: In function ‘dwmci_prepare_data’:
drivers/mmc/dw_mmc.c:61:35: warning: cast from pointer to integer
of different size [-Wpointer-to-int-cast]
  dwmci_writel(host, DWMCI_DBADDR, (unsigned int)cur_idmac);
                                   ^
drivers/mmc/dw_mmc.c:73:9: warning: cast from pointer to integer
of different size [-Wpointer-to-int-cast]
         (u32)bounce_buffer + (i * PAGE_SIZE));
         ^
  CC      drivers/mmc/hi6220_dw_mmc.o
drivers/mmc/hi6220_dw_mmc.c: In function ‘hi6220_dwmci_add_port’:
drivers/mmc/hi6220_dw_mmc.c:51:17: warning: cast to pointer from integer
of different size [-Wint-to-pointer-cast]
  host->ioaddr = (void *)regbase;

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>