Adding regulator driver for the device mpq7920.
The MPQ7920 PMIC device contains four DC-DC buck converters and
five regulators, is designed for automotive and accessed over I2C.

Fixed sparse warning reported on this patch
Reported-by: Nkbuild test robot <lkp@intel.com>
Signed-off-by: NSaravanan Sekar <sravanhome@gmail.com>
Link: https://lore.kernel.org/r/20200109195346.30270-1-sravanhome@gmail.comSigned-off-by: NMark Brown <broonie@kernel.org>