video: tegra: dc: change vrr native mode location

video: tegra: dc: change vrr native mode location

Change VRR native mode location from mode list index
VRR_NATIVE_MODE_IDX to the last mode in the list. This
matches bootloader behavior.

Bug 1645593

Change-Id: I79f17c80d846cc236b0dd8c8f4874c2daf863894
Signed-off-by: Daniel Solomon <daniels@nvidia.com>
Reviewed-on: http://git-master/r/744705
(cherry picked from commit 860c86538feb0febace6305510e894580f1176c2)
Reviewed-on: http://git-master/r/751050
Reviewed-by: Mitch Luban <mluban@nvidia.com>
Tested-by: Mitch Luban <mluban@nvidia.com>