drm/radeon/kms/atom: fix PHY init

The PHY was not initialized correctly after
ac89af1e since
the function bailed early as an encoder was not
assigned.  The encoder isn't necessary for PHY init
so just assign to 0 for init so that the table
is executed.

Reported-by: Ari Savolainen <ari.m.savolainen@gmail.com>
Tested-by: Ari Savolainen <ari.m.savolainen@gmail.com>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>