clk: pistachio: Include clk.h

This clock provider uses the consumer API, so include clk.h
explicitly.

Cc: Andrew Bresticker <abrestic@chromium.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/pistachio/clk.c

@@ -6,6 +6,7 @@
  * version 2, as published by the Free Software Foundation.
  */
 
+#include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/kernel.h>
 #include <linux/of.h>