qpnp-fg-gen3: fix reading OCV and Vbatt predicted values

Open circuit voltage and predicted battery voltage are read from
16 bits. However, the real value is present only in 15 bits.
Mask the bit 16 to get the proper readings.

Change-Id: I196ccc64fd221fead87a88f43dce1a21ba800908
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>