mfd/rtc/gpio: twl: No need to allocate bigger buffer for write

Since the twl-core has been converted to use regmap it is no longer needed
to allocate bigger buffer for data when writing to twl.

CC: Grant Likely <grant.likely@secretlab.ca>
CC: Alessandro Zummo <a.zummo@towertech.it>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>