gpio: uapi: fix line info flags description

The description of the flags field of the struct gpio_v2_line_info
mentions "the GPIO lines" while the info only applies to an individual
GPIO line.  This was accidentally changed from "the GPIO line" during
formatting improvements.

Reword to "this GPIO line" to clarify and to be consistent with other
struct gpio_v2_line_info fields.

Fixes: 2cc522d3 ("gpio: uapi: kernel-doc formatting improvements")
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>