power: supply: max17040: fix null-ptr-deref in max17040_probe()

Add check the return value of devm_regmap_init_i2c(), otherwise
later access may cause null-ptr-deref as follows:

KASAN: null-ptr-deref in range [0x0000000000000360-0x0000000000000367]
RIP: 0010:regmap_read+0x33/0x170
Call Trace:
max17040_probe+0x61b/0xff0 [max17040_battery]
? write_comp_data+0x2a/0x90
? max17040_set_property+0x1d0/0x1d0 [max17040_battery]
? tracer_hardirqs_on+0x33/0x520
? __sanitizer_cov_trace_pc+0x1d/0x50
? _raw_spin_unlock_irqrestore+0x4b/0x60
? trace_hardirqs_on+0x63/0x2d0
? write_comp_data+0x2a/0x90
? __sanitizer_cov_trace_pc+0x1d/0x50
? max17040_set_property+0x1d0/0x1d0 [max17040_battery]
i2c_device_probe+0xa31/0xbe0

Fixes: 6455a8a84bdf ("power: supply: max17040: Use regmap i2c")
Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Yang Yingliang <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/max17040_battery.c

···
 
 	chip->client = client;
 	chip->regmap = devm_regmap_init_i2c(client, &max17040_regmap);
+	if (IS_ERR(chip->regmap))
+		return PTR_ERR(chip->regmap);
 	chip_id = (enum chip_id) id->driver_data;
 	if (client->dev.of_node) {
 		ret = max17040_get_of_data(chip);