gpio: reinforce desc->flags handling

We now removed the gpio_lock spinlock and modified the places
previously protected by it to handle desc->flags access in a consistent
way. Let's improve other places that were previously unprotected by
reading the flags field of gpio_desc once and using the stored value for
logic consistency. If we need to modify the field, let's also write it
back once with a consistent value resulting from the function's logic.

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