gpio: f7188x: fix edit mistake

Fix a typo causing a build regression.

Fixes: f90c6bdb

 ("gpio: f7188x: use the new open drain callback")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>