asoc: codecs: add null pointer check for swr control data

Null check is needed before accessing swr control data
to ensure proper error handling in case speaker path
is issued when swr is not enabled.

Change-Id: I5037a912652189b3ae58f1119d0534777a9c264a
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>