ASoC: msm: qdsp6v2: avoid null pointer dereference

If memory allocation fails or allocation of extremely
large buffer is attempted causing kmalloc to return a
NULL, the present code goes ahead and dereferences the
NULL pointer.
The change returns from the function immediately if
kmalloc returns a NULL.

CRs-Fixed: 683684
Change-Id: Iffd532b9eacebfc3c365ced6856a117164111988
Signed-off-by: Aravind Kumar <akumark@codeaurora.org>