power_supply: bq27x00: fix temperature conversion

The power supply class requires tenths of degree Celsius.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>