ARM: dts: msm: enable WA for IPA channel 20 for msmcobalt

Update IPA node to not not use IPA channel 20 due to hardware limitation.

Change-Id: Id849055526bf70e0cc8161239b4530a7fc575744
CRs-Fixed: 1005061
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>