pci: xgene: do not use clk-private.h

The X-Gene PCIe driver consumes clocks and does not provide them.
Replace usage of clk-private.h with clk.h.

Cc: Tanmay Inamdar <[e-mail]>
Signed-off-by: Michael Turquette <[e-mail]>

drivers/pci/host/pci-xgene.c

···
  * GNU General Public License for more details.
  *
  */
-#include <linux/clk-private.h>
+#include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/io.h>
 #include <linux/jiffies.h>