staging: greybus: audio: Resolve compilation error in topology parser

Fix compilation errors for GB Audio topology parser code with recent
kernel versions.
Signed-off-by: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/2542330352ae1d01469a616ea45edb461615e072.1594290158.git.vaibhav.sr@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>