qcom-charger: qpnp-fg: fix oob array access and uninitialized return

pos is incremented by bytes_read which could exceed the boundary of
kbuf. Fix this by checking the bounds of pos.

resched_ms is used when uninitialized. Initialize it.

Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>
Change-Id: I3a01d59bb5ed53666307a5210a684c7d9fd654fc