battery: reduce overall FCC in taper stepper algorithm

Currently the code steps down 25% from the parallel charger's share
during taper phase. Change that to reduce 200mA from the entire FCC
instead. This ensures that the battery would enter fast chg regardless
of the current distribution between them.

Change-Id: I8a0a282c52a5f8a60e8f6bc4337379645ef85c9b
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>