mmc: dw_mmc: Remove unused function for !CONFIG_OF

dw_mci_of_find_slot_node() is only used in dw_mci_of_get_slot_quirks()
if CONFIG_OF is defined, thus there is no need to have a !CONFIG_OF
version of it. Fixes the following compile warning with !CONFIG_OF:

  CC [M]  drivers/mmc/host/dw_mmc.o
drivers/mmc/host/dw_mmc.c:2223:28: warning: ‘dw_mci_of_find_slot_node’ defined but not used [-Wunused-function]
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/dw_mmc.c

@@ -2220,10 +2220,6 @@ static int dw_mci_of_get_slot_quirks(struct device *dev, u8 slot)
 {
 	return 0;
 }
-static struct device_node *dw_mci_of_find_slot_node(struct device *dev, u8 slot)
-{
-	return NULL;
-}
 #endif /* CONFIG_OF */
 
 static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)