msm: ais: mem: Validate return value of dma_buf_get

After ion allocation dma_buf_get called to increase the ref count.
Validation is required to know the dma_buf_get success or not.

Change-Id: I86724a17583ca29b509434065477b3aec421ada3
Signed-off-by: E V Ravi <evenka@codeaurora.org>