PCI: xgene: Include clk.h instead of clk-private.h

This driver should be including clk.h as it's a clock consumer, not a clock
provider that needs to register clocks early.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Tanmay Inamdar <tinamdar@apm.com>