clk_k210.c: Clean up how we handle nop

Now that sandbox has <asm/barrier.h> and defines nop() there we should
include that in our driver for clarity and then remove our local nop()
from <k210/pll.h>.

Reviewed-by: Sean Anderson <seanga2@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/clk/clk_k210.c b/drivers/clk/clk_k210.c
index c534cc0..b9469b9 100644
--- a/drivers/clk/clk_k210.c
+++ b/drivers/clk/clk_k210.c
@@ -16,6 +16,7 @@
 #include <dt-bindings/mfd/k210-sysctl.h>
 #include <k210/pll.h>
 #include <linux/bitfield.h>
+#include <asm/barrier.h>
 
 DECLARE_GLOBAL_DATA_PTR;