pinctrl: Flag strict is a field in struct pinmux_ops

Documentation incorrectly refers to struct pinctrl_desc, where no such flag is
available. Replace the name of the struct.

Fixes: commit 8c4c2016 ("pinctrl: move strict option to pinmux_ops")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>