clk: kendryte/pll.h: do not redefine nop()

The kendryte PLL code uses nop as barrier. The macro is not defined for
the sandbox on x86 but is defined on RISC-V.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>

include/kendryte/pll.h

@@ -7,6 +7,7 @@
 
 #include <clk.h>
 #include <test/export.h>
+#include <asm/io.h>
 
 #define K210_PLL_CLKR GENMASK(3, 0)
 #define K210_PLL_CLKF GENMASK(9, 4)
@@ -43,9 +44,13 @@ struct k210_pll_config {
 #ifdef CONFIG_UNIT_TEST
 TEST_STATIC int k210_pll_calc_config(u32 rate, u32 rate_in,
 				     struct k210_pll_config *best);
+
+#ifndef nop
 #define nop()
 #endif
 
+#endif
+
 extern const struct clk_ops k210_pll_ops;
 
 struct clk *k210_register_pll_struct(const char *name, const char *parent_name,