power: qpnp-bms: use battery backed data registers to store soc

Switch from using data_reg_2 to using data_reg_1 for storing shutdown
soc in order to leverage data_reg_0 being battery backed. This way when
a battery is inserted, the BMS will not remember the shutdown soc and
force a wrong value.

Change-Id: I1b79e28d7da133cf78064028ba2786979b37f198
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>