asoc: routing: Fix routing entries of Multimedia20 mixer

Add routing entries for Multimedia20 Tx mixer in
order to fix boot up warnings in routing driver.

CRs-Fixed: 2281591
Change-Id: I9ac35dab53811bd6ede64d69d221cdc6fbd622f4
Signed-off-by: Aditya Bavanari <abavanar@codeaurora.org>