mmc: sdhci: Fix crash on boot with C0 stepping Moorestown platforms

SDHC2 is newly added in C0 stepping of Langwell. Without the Moorestown
specific quirk, the default pci_probe will be called and crash the kernel.

This patch unblocks the crash problem on C0 by using the same probing
function as HC1, which limits the number of slots to one.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>