gpio: twl4030: Use only TWL4030_MODULE_LED for LED configuration

Avoid using the TWL4030_MODULE_PWMA/B as module ID. The LEDEN, PWMA ON/OFF
and PWMB ON/OFF registers are in a continuous range starting from LED base.
This is going to be helpful for further cleanup in the twl stack.

No functional changes.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>