exynos: fix G2D_DOUBLE_TO_FIXED for non-integer input

The hardware accepts scaling factors formatted in a
fixed-point format. The current macro casts to integer
first, then multiplies by the fp conversion factor.

This does not make any sense. In particular, truly
'fractional' inputs, like 1.5, won't work that way.

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