regulator: bd718xx: fix build warning on x86_64

Casting address to unsigned int causes a warning on some 64 bit
architectures. Fix the cast.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@kernel.org>