drm/exynos: fix kcalloc size of g2d cmdlist node

The size argument means just one element size when we call kcalloc, so
G2D_CMDLIST_NUM * sizeof(*node) is wrong.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>