sdhci: handle hot-remove

Gracefully handle when the device is suddenly removed. Do a test read
and avoid any further access if that read returns -1.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

diff --cc drivers/mmc/host/sdhci-pci.c
Simple merge

diff --cc drivers/mmc/host/sdhci.c
Simple merge

diff --cc drivers/mmc/host/sdhci.h
Simple merge