battery: disable parallel at end of taper stepper

Currently, taper stepper algorithm exits once parallel's share falls
below 500mA. However, the next FCC change ends up enabling taper
stepper algorithm.

Fix it by casting a disable vote at the end of taper stepper.

Change-Id: I6aa66508eb2a8cf9b0c6d9e82d1463ca7daa1464
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>