drm/exynos: fix memory leak to EDID block

drm_get_edid() returns a pointer to an EDID block. The caller
is responsible to free this pointer itself.
Here the pointer gets assigned to the local variable raw_edid.
Therefore it should be freed before the variable goes out of
scope.

Change-Id: I00765070377118178c513651fb46c8bb562e71ed
Signed-off-by: Egbert Eich <eich@suse.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>