drm/bridge: vga-dac: Fix edid memory leak

edid should be freed once it's finished being used.

Fixes: 56fe8b6f

 ("drm/bridge: Add RGB to VGA bridge support")
Cc: Rob Herring <robh@kernel.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: <stable@vger.kernel.org> # v4.9+
Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180420190007.1572-1-seanpaul@chromium.org