drm: atmel-hlcdc: Fix vertical scaling

The code is applying the same scaling for the X and Y components,
thus making the scaling feature only functional when both components
have the same scaling factor.

Do the s/_w/_h/ replacement where appropriate to fix vertical scaling.

Signed-off-by: Jan Leupold <leupold@rsi-elektrotechnik.de>
Fixes: 1a396789 ("drm: add Atmel HLCDC Display Controller support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>