OMAP3: Correct name of omap34xx_gpios when using DM_GPIO

The name of the gpio bank under DM_GPIO appear to be a copy-paste error.
This changes the name of the gpio bank from am33xx_gpios to omap34xx_gpios.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>