power: bq27xxx_battery: Restore device name

Patch <703df6c0> ("power: bq27xxx_battery: Reorganize I2C
into a module") has removed the device name numbering from
bq27xxx_battery_i2c_probe. Fix that by restoring the code.

Fixes: 703df6c0
Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>