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>