exynos: fix scaling factor computation in g2d_copy_with_scale

When division of source and destination width yields the
scaling factor for the x-coordinate, then it should be
source/destination _height_ for y.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>