gpio: twl4030: Fix passing of pdata in the device tree case

We still have some legacy code needing the callback functions
that won't work properly without platform data. To use platform
data for twl4030-gpio, we need to not trash the possible data.

Cc: linux-gpio@vger.kernel.org
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
[tony@atomide.com: folded in fix from Fengguang to use struct assignment]
Signed-off-by: Tony Lindgren <tony@atomide.com>