ASoC: msm: qdsp6v2: Fix information leak in kernel

In function msm_routing_set_downmix_control_data,
a negative value of be_id from userspace can bypass
the bounds check and thus result in information
leak to the userspace. Fix it by introducing a
lower bound.

CRs-fixed: 2120551
Change-Id: Idf82b38d58939645e69ebd6bac400ac3da19f187
Signed-off-by: Tanya Dixit <tdixit@codeaurora.org>