gpio: uapi: Improve phrasing around arrays representing empty strings

Character arrays can be considered empty strings (if they are
immediately terminated), but they cannot be NULL.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

include/uapi/linux/gpio.h

@@ -18,7 +18,7 @@
  * struct gpiochip_info - Information about a certain GPIO chip
  * @name: the Linux kernel name of this GPIO chip
  * @label: a functional name for this GPIO chip, such as a product
- * number, may be NULL
+ * number, may be empty
  * @lines: number of GPIO lines on this chip
  */
 struct gpiochip_info {
@@ -44,10 +44,10 @@ struct gpiochip_info {
  * @flags: various flags for this line
  * @name: the name of this GPIO line, such as the output pin of the line on the
  * chip, a rail or a pin header name on a board, as specified by the gpio
- * chip, may be NULL
+ * chip, may be empty
  * @consumer: a functional name for the consumer of this GPIO line as set by
- * whatever is using it, will be NULL if there is no current user but may
- * also be NULL if the consumer doesn't set this up
+ * whatever is using it, will be empty if there is no current user but may
+ * also be empty if the consumer doesn't set this up
  */
 struct gpioline_info {
 	__u32 line_offset;