gpio: max7301: Reverting "Do not force SPI speed when using OF Platform"

This patch reverts commit 047b93a3 which breaks
MAX7301 GPIO driver because that commit was dependant on a rejected patch that
was implementing selection of SPI speed from the Device Tree.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>