Fix comment on pinctrl_gpio_range.pin_base

The comment introduced with the recently added pinctrl_gpio_range.pins
element was wrong. This corrects it.
Thanks to Patrice Chotard for pointing this out.
Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/pinctrl/pinctrl.h

@@ -49,7 +49,7 @@ struct pinctrl_pin_desc {
  * @name: a name for the chip in this range
  * @id: an ID number for the chip in this range
  * @base: base offset of the GPIO range
- * @pin_base: base pin number of the GPIO range if pins != NULL
+ * @pin_base: base pin number of the GPIO range if pins == NULL
  * @pins: enumeration of pins in GPIO range or NULL
  * @npins: number of pins in the GPIO range, including the base number
  * @gc: an optional pointer to a gpio_chip