drm/exynos: remove redundant devm_kfree()

There is no need for explicit calls of devm_kfree(), as
the allocated memory will be freed during driver's detach.
Remove the redundant devm_kfree() calls from probe() and
remove() callbacks.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>