drm/arm: mali-dp: Fix error return code in malidp_bind()

Fix to return error code -EINVAL from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: 3c31760e

 ('drm/arm: mali-dp: Set crtc.port to the port
instead of the endpoint')
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Brian Starkey <brian.starkey@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1469672066-13401-1-git-send-email-weiyj.lk@gmail.com