sw5100_bms: shutdown soc offset / reserve round up.

Replace truncation due to integer division with round up so that 99% is
properly modeled on the soc offset / reserve scale. Also correct for
possibility of division by zero or negative value.

Bug: 306380628
Test: Confirm healthd SOC percentage reaches 99%.
(cherry picked from https://partner-android-review.googlesource.com/q/commit:837fe047d049754272f00a2c90e5ae749f137d51)
Merged-In: Ibad6b75c6ce5088f32b10cb92e23890e5a15b705
Change-Id: Ibad6b75c6ce5088f32b10cb92e23890e5a15b705
1 file changed