regulator: da9121: Fix uninit-value in da9121_assign_chip_model()

KASAN report slab-out-of-bounds in __regmap_init as follows:

BUG: KASAN: slab-out-of-bounds in __regmap_init drivers/base/regmap/regmap.c:841
Read of size 1 at addr ffff88803678cdf1 by task xrun/9137

CPU: 0 PID: 9137 Comm: xrun Tainted: G        W         5.18.0-rc2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x15a lib/dump_stack.c:88
 print_report.cold+0xcd/0x69b mm/kasan/report.c:313
 kasan_report+0x8e/0xc0 mm/kasan/report.c:491
 __regmap_init+0x4540/0x4ba0 drivers/base/regmap/regmap.c:841
 __devm_regmap_init+0x7a/0x100 drivers/base/regmap/regmap.c:1266
 __devm_regmap_init_i2c+0x65/0x80 drivers/base/regmap/regmap-i2c.c:394
 da9121_i2c_probe+0x386/0x6d1 drivers/regulator/da9121-regulator.c:1039
 i2c_device_probe+0x959/0xac0 drivers/i2c/i2c-core-base.c:563

This happend when da9121 device is probe by da9121_i2c_id, but with
invalid dts. Thus, chip->subvariant_id is set to -EINVAL, and later
da9121_assign_chip_model() will access 'regmap' without init it.

Fix it by return -EINVAL from da9121_assign_chip_model() if
'chip->subvariant_id' is invalid.

Fixes: f3fbd556 ("regulator: da9121: Add device variants")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Adam Ward <Adam.Ward.Opensource@diasemi.com>
Link: https://lore.kernel.org/r/20220421090335.1876149-1-weiyongjun1@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/da9121-regulator.c

@@ -1030,6 +1030,8 @@ static int da9121_assign_chip_model(struct i2c_client *i2c,
 		chip->variant_id = DA9121_TYPE_DA9142;
 		regmap = &da9121_2ch_regmap_config;
 		break;
+	default:
+		return -EINVAL;
 	}
 
 	/* Set these up for of_regulator_match call which may want .of_map_modes */