mmc: sdhci-pci: Do not set DMA mask in enable_dma()

DMA mask will already be set by sdhci_set_dma_mask(), which
is equivalent to the removed code since pci_set_dma_mask()
expands to its DMA-API counterpart.

There should also be no reason to set the DMA mask after probe.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>