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>