ARM: dts: msm: Fix the board subtype for sxr1120 external codec

There was incorrect board subtype value for sxr1120-external-codec
in DT, which was resulting in incorrect DT picking. Fix this by
correct board subtype value.

Change-Id: Ieb86013647f4e8f0e6c7909634dd90e0592fe2f4
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>