msm: camera: 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: I1c22b59bbbf9fa5bfe5282217cf1280ea3a265a7
Signed-off-by: Ravikishore Pampana <rpampana@codeaurora.org>