staging: hikey9xx: Kconfig: add regulator dependency

The regulator driver needs it, as otherwise it will produce
errors when creating vmlinux.

Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/a287238bd0141aa68aae7d4cec4c1174a43b3e53.1597766680.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>