power: qpnp-qg: Add range checks to FIFO length

In some erroneous cases there could be back-to-back
calls to process the accumulator data which may lead
to a array overflow. Fix this by adding range check
while populating the FIFO data.

Change-Id: I3f2495649153ae16040579b71dff5b78315b29a9
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>