power: supply: axp288_fuel_gauge: Report register-address on readb / writeb errors

When fuel_gauge_reg_readb()/_writeb() fails, report which register we
were trying to read / write when the error happened.

Also reword the message a bit:
- Drop the axp288 prefix, dev_err() already prints this
- Switch from telegram / abbreviated style to a normal sentence, aligning
  the message with those from fuel_gauge_read_*bit_word()
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/axp288_fuel_gauge.c

@@ -142,7 +142,7 @@ static int fuel_gauge_reg_readb(struct axp288_fg_info *info, int reg)
 	}
 
 	if (ret < 0) {
-		dev_err(&info->pdev->dev, "axp288 reg read err:%d\n", ret);
+		dev_err(&info->pdev->dev, "Error reading reg 0x%02x err: %d\n", reg, ret);
 		return ret;
 	}
 
@@ -156,7 +156,7 @@ static int fuel_gauge_reg_writeb(struct axp288_fg_info *info, int reg, u8 val)
 	ret = regmap_write(info->regmap, reg, (unsigned int)val);
 
 	if (ret < 0)
-		dev_err(&info->pdev->dev, "axp288 reg write err:%d\n", ret);
+		dev_err(&info->pdev->dev, "Error writing reg 0x%02x err: %d\n", reg, ret);
 
 	return ret;
 }