ide: remove ->mmio flag from ide_hwif_t

Since scc_pata host driver no longer uses IDE PCI layer / ide_dma_setup()
and all other ->mmio users set also IDE_HFLAG_MMIO host flag we can safely
remove ->mmio flag.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>