drm/amd/display: Only set PSR version when valid

[Why]
DMCUB will hang if we send a PSR unsupported set version command.

This can occur if we fall-through into the default case in the switch
statement for PSR version.

[How]
Add an unsupported check after the switch statement.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>