drm/radeon: Don't drop DP 2.7 Ghz link setup on some cards.

As observed on Apple iMac10,1, DCE-3.2, RV-730,
link rate of 2.7 Ghz is not selected, because
the args.v1.ucConfig flag setting for 2.7 Ghz
gets overwritten by a following assignment of
the transmitter to use.

Move link rate setup a few lines down to fix this.
In practice this didn't have any positive or
negative effect on display setup on the tested
iMac10,1 so i don't know if backporting to stable
makes sense or not.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org