power: qpnp-vm-bms: Fix minor issues in VM BMS

1. SPMI cannot access > 8 bytes of data in a single read.
Fix the FIFO read by reading one-byte at a time.

2. Fix force_fsm_mode by disabling all other modes while forcing
a particular mode.

3. Use proper data type to calculate VBAT from raw ADC values.

4. Fix logging format

Change-Id: I9525da3747ac50908125d035f87dc3eda14029c8
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>