smb-lib: update displaying battery overvoltage in health property

Currently, smb2 charger is configured to not end the charging
cycle when battery overvoltage occurs. However, when the battery
overvoltage status is read, it will be displayed through health
property. Improve this by reading the battery voltage and check
whether it is within 40mV headroom above float voltage. If it is
above that threshold then continue with displaying overvoltage
status.

CRs-Fixed: 1079363
Change-Id: I45847f446c91c80a5110d80b59a0ae4b8e2c40e5
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>