ASoC: msm: Fix for null pointer dereference

Check for the pointer returned by cdev_alloc() to
make sure it is not NULL before dereferencing it.

Change-Id: Ie97d4ec1dfa9c2b6e077fa7d63c8d764b91f0c9c
Signed-off-by: Vicky Sehrawat <vickys@codeaurora.org>