drm/atomic: put state on error path

Put the state before returning error code.

Fixes: 44596b8c ("drm/atomic: Unify conflicting encoder handling.")
Signed-off-by: Pan Bian <bianpan2016@163.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210119121127.84127-1-bianpan2016@163.com