Staging: fbtft: Fix probing of gpio descriptor

Conversion to use gpio descriptors broke all gpio lookups as
devm_gpiod_get_index was converted to use dev->driver->name for
the gpio name lookup. Fix this by using the name param. In
addition gpiod_get post-fixes the -gpios to the name so that
shouldn't be included in the call. However this then breaks the
of_find_property call to see if the gpio entry exists as all
fbtft treats all gpios as optional. So use devm_gpiod_get_index_optional
instead which achieves the same thing and is simpler.

Nishad confirmed the changes where only ever compile tested.

Fixes: c440eee1 ("Staging: fbtft: Switch to the gpio descriptor interface")
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Jan Sebastian Götte <linux@jaseg.net>
Signed-off-by: Phil Reid <preid@electromag.com.au>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1563236677-5045-2-git-send-email-preid@electromag.com.au


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>