pdc202xx_new: add missing ->dma_base check

If ->dma_base is not set (== PCI BAR4 cannot be reserved) then DMA hooks
shouldn't be initialized or bad things will happen.

Also this host driver requires valid PCI BAR4 for normal operation so
check it in ->init_chipset and fail initialization if not set.

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