mmc: pci: Drop the superfluous cast

dm_pci_map_bar() return a value of (void *) already, hence no need
to cast it again before assigning to host->ioaddr.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>