drm/exynos: remove redundant assignment to pointer 'node'

The pointer 'node' is being assigned with a value that is never
read and is re-assigned later. The assignment is redundant and
can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Inki Dae <daeinki@gmail.com>