input: qcom-hv-haptics: fix out of bound of FIFO samples array

When calculating play length for FIFO play, it is out of bound
of the FIFO samples array. Fix it.

Change-Id: I8ad458802a0070f493ac53160ab90a6cf648d9e7
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>