ASoC: qdsp6v2: handle ion alloc failure correctly

When ion alloc fails for audio or system heap, an
error pointer is returned which gets dereferenced
causing a crash.
Get the error number from the error pointer returned
using the PTR_ERR api.

CRs-Fixed: 799946
Change-Id: Ic96738cdf8fe8fa8ef4767081846d77173fdd3b7
Signed-off-by: Aravind Kumar <akumark@codeaurora.org>