sdhci: fix the PCI device, using the PCI address space for DMA

While SysBus devices can use the get_system_memory() address space,
PCI devices should use the bus master address space for DMA.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20180115182436.2066-14-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>