qcom: vpu: restore compatibility with kernels before 6.6

qcom: vpu: restore compatibility with kernels before 6.6

Linux kernels before 6.6 used qcom/vpu-1.0/venus.mdt as a firmware
filename for Qualcomm SM8250 devices. Commit 36db650dae03 ("qcom: update
path for video firmware for vpu-1/2/3.0") moved the VPU firmware, added
the venus.mbn compatibility symlink, but at the same time it dropped
the venus.mdt symlink. Bring the historical name back to restore
compatibility with kernels older than 6.6.

Fixes: 36db650dae03 ("qcom: update path for video firmware for vpu-1/2/3.0")
Cc: Dikshita Agarwal <quic_dikshita@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Josh Boyer <jwboyer@kernel.org>