power: supply: bq25980: Fix uninitialized wd_reg_val

Fix the uninitialized wd_reg_val if the for..loop was not successful in
finding an appropriate match.

Fixes: 5069185f ("power: supply: bq25980: Add support for the BQ259xx family")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>