battery: reduce SMB only for taper stepper

Currently the driver moves FCC to PMI as it steps down
from SMB. Instead we should step down just the SMB.

Change-Id: I7ad9ca4364a44bacb539f8b045cf97f7945155f5
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>