power: pm8921-bms: dont use override mode if batfet is open

If the battery fet is open, the current sourced or sinked from the
battery is very low. There is a high chance that an open circuit
voltage(OCV) happens. Putting the BMS in override mode resets the timer
whose expiry causes an OCV.

Avoid putting the BMS in override mode if battery fet is open.

Change-Id: Idc463bcc55b51cf188cc8ee440a66f763654f174
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>