drm/amd/display: Incorrect Mirror Cositing

drm/amd/display: Incorrect Mirror Cositing

[WHY]
hinit/vinit are incorrect in the case of mirroring.

[HOW]
Cositing sign must be flipped when image is mirrored in the vertical
or horizontal direction.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Samson Tam <samson.tam@amd.com>
Signed-off-by: Jesse Agate <jesse.agate@amd.com>
Signed-off-by: Brendan Leder <breleder@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>