docs: driver-api: gpio: Fix some typos

Correct some simple spelling mistakes in consumer.rst, driver.rst
and using-gpio.rst.

Signed-off-by: Tom Schwindl <schwindl@posteo.de>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/YrTdAv3YPlCiDr2u@posteo.de


Signed-off-by: Jonathan Corbet <corbet@lwn.net>