drm/rockchip: dw-mipi-dsi: fix possible un-balanced runtime PM enable

In the case where the bind gets deferred we would end up with a
un-balanced runtime PM enable call.

Fix this by simply moving the pm_runtime_enable call to the end of
the bind function when all paths have succeeded.

Signed-off-by: Mirza Krak <mirza.krak@endian.se>
Signed-off-by: Sandy Huang <hjc@rock-chips.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1510734286-37434-1-git-send-email-mirza.krak@endian.se