drm/exynos: Fix dma_parms allocation

Since commit 9495b7e9

 ("driver core: platform: Initialize dma_parms
for platform devices") driver core handles allocation of the dma_parms
structure for platform device, so there is no need to manually allocate
nor free it.

Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>