dsp: msm_audio_ion: use dma_buf_vmap for mapping dma_buf to kernel

Use the newly added dma_buf_vmap API for mapping a dma_buf
to kernel address space.

Change-Id: Idacada71eb827b4af96a793a180456ae910e30e8
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>