mfd: ab8500: Export ab8500_gpadc_sw_hw_convert properly

Apparently the ab8500_gpadc_sw_hw_convert function got renamed
from ab8500_gpadc_convert to ab8500_gpadc_sw_hw_convert in
commit 73482346

 "mfd: ab8500-gpadc: Add gpadc hw conversion",
but the export for this function did not get changed at the
same time, causing this allyesconfig error:

ERROR: "ab8500_gpadc_sw_hw_convert" [drivers/hwmon/ab8500.ko] undefined!

This patch fixes the export.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: M'boumba Cedric Madianga <cedric.madianga@stericsson.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Mattias WALLIN <mattias.wallin@stericsson.com>
Cc: Michel JAOUEN <michel.jaouen@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>