greybus: db3-platform: fix code that fetches reset GPIO

The code that fetches the reset GPIO for an AP bridge suffers
from an apparent copy/paste error.  Fix it.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>