power: bq24257: Add bit definition for temp sense enable

Adding a missing bit definition for the sake of consistency device model
vs. bit field representation. No change in functionality.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>