pinctrl: st: Drop wrong kernel doc annotations

Kernel doc validator is not happy:

  .../pinctrl-st.c:59: warning: This comment starts with '/**', but isn't a kernel-doc comment.
  .../pinctrl-st.c:73: warning: This comment starts with '/**', but isn't a kernel-doc comment.

Drop them as they are indeed not a kernel doc comments.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>