regulator: mp8859: add supply entry

Add vin_supply to the regulator description to support a nice
regulator tree.
Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20200203110034.1448-1-m.reichl@fivetechno.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/mp8859.c

@@ -95,6 +95,7 @@ static const struct regulator_desc mp8859_regulators[] = {
 		.id = 0,
 		.type = REGULATOR_VOLTAGE,
 		.name = "mp8859_dcdc",
+		.supply_name = "vin",
 		.of_match = of_match_ptr("mp8859_dcdc"),
 		.n_voltages = VOL_MAX_IDX + 1,
 		.linear_ranges = mp8859_dcdc_ranges,