power: pm8921-bms: update real fcc if within 3% of previous fcc

An issue was observed when the calculated (real fcc) fcc was very low
as compared to fcc. Usually the fcc should not drop/increase beyond 3%
per charge cycle.

Update the code to check the delta between calculated fcc and the previous
fcc and update the real fcc if delta is within 3 percent.

Change-Id: Ib3ab383971fbd86af91c642ac5a2a38cbb555d9f
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>