msm: vidc: Fix criteria for hierp num_ref calc

[1] num_ref for hierp has to be calculated only if
    max_layer value is > 1. Since max_layer value
    0/1 indicates absence of layer encoding.
[2] Fix hybrid_hp num_ref calculation inline with
    FW calc

Change-Id: I507d58c33529e5976974cc2d5a6e2d3fd8c55026
Signed-off-by: Priyanka Gujjula <pgujjula@codeaurora.org>