drm/amd/pm: no need to force MCLK to highest when no display connected

drm/amd/pm: no need to force MCLK to highest when no display connected

BugLink: https://bugs.launchpad.net/bugs/1923069
commit acc7baafeb0b52a5b91be64c4776f827a163dda1 upstream.

Correct the check for vblank short.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>