pinctrl/rockchip: Drop wrong kernel doc annotation

Kernel doc validator is not happy:

  .../pinctrl-rockchip.c:45: warning: This comment starts with '/**', but isn't a kernel-doc comment.

Drop it as it's indeed not a kernel doc comment.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>

drivers/pinctrl/pinctrl-rockchip.c

@@ -39,7 +39,7 @@
 #include "pinconf.h"
 #include "pinctrl-rockchip.h"
 
-/**
+/*
  * Generate a bitmask for setting a value (v) with a write mask bit in hiword
  * register 31:16 area.
  */