ASoC: wcd9320: Avoid NULL pointer access

It is possible that taiko private data will
be accessed without creating memory when
sound card is not registered. Avoid kernel
crash by checking it for NULL and return without
access.

CRs-Fixed: 626673
Change-Id: I88523b352f251817697ac4c4fff82d750e5af618
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>