regulator: ab3100: cast fix

The AB3100 regulator driver emits a warning when compiled on 64bit
systems like this:

drivers/regulator/ab3100.c:
In function ‘ab3100_regulator_of_probe’:
srivers/regulator/ab3100.c:649:4:
warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

As the int is a different size than the 64bit pointer used to
pass regulator data. Switch to using an unsigned long as ID
passed for the regulator to get rid of the warning.

Reported-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>