drm/armada: Fix a potential double free in an error handling path

'priv' is a managed resource, so there is no need to free it explicitly or
there will be a double free().

Fixes: 90ad200b ("drm/armada: Use devm_drm_dev_alloc")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/c4f3c9207a9fce35cb6dd2cc60e755275961588a.1640536364.git.christophe.jaillet@wanadoo.fr