sdhci-pxav3: Fix runtime PM initialization

Commit bb691ae4

 breaks boot on OLPC
XO-4, it hangs somewhere inside sdhci_add_host.

When pm_runtime_set_autosuspend_delay() was being called, the device's
usage counter was 0, causing the PM layer to runtime-suspend the
device.  We then went on to call sdhci_add_host() on a suspended
device, which hung.

Fix this by making the driver consistent with the omap_hsmmc driver,
both in terms of runtime PM initialization and error handling. Now
the device is not runtime-suspended until we exit the probe routine.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Chris Ball <cjb@laptop.org>