staging: regulator: hi6421v600-regulator: initialize ramp_delay

Without that, the regulator's core complains with:

       ldo17: ramp_delay not set

For now, use the enable time, as we don't have any datasheets from
this device.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/67df5456e4f23c88ab4fd9331eb8202c3952e5c5.1597647359.git.mchehab+huawei@kernel.org


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