include/hw/qdev-core.h: Correct and clarify gpio doc comments

include/hw/qdev-core.h: Correct and clarify gpio doc comments

The doc comments for the functions for named GPIO inputs and
outputs had a couple of problems:
 * some copy-and-paste errors meant the qdev_connect_gpio_out_named()
   doc comment had references to input GPIOs that should be to
   output GPIOs
 * it wasn't very clear that named GPIOs are arrays and so the
   connect functions specify a single GPIO line by giving both
   the name of the array and the index within that array

Fix the copy-and-paste errors and slightly expand the text
to say that functions are connecting one line in a named GPIO
array, not a single named GPIO line.

Reported-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240708153312.3109380-1-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>