mmc: sdhci-pltfm: dt device does not pass parent to sdhci_alloc_host

Neither platform based nor dt based device needs to pass the parent
to sdhci_alloc_host.  There is no difference between platform and dt
on this point.

The patch makes the change to pass device itself than its parent to
sdhci_alloc_host for dt case too.  Otherwise the probe function of
sdhci based drivers which is shared between platform and dt will
fail on dt case.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: Chris Ball <cjb@laptop.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Chris Ball <cjb@laptop.org>