staging: greybus: audio_manager: fix a missing check of ida_simple_get

ida_simple_get could fail. The fix inserts a check for its
return value.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Reviewed-by: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>