drm/rockchip: dsi: Fix duplicate included linux/phy/phy.h

Clean up the following includecheck warning:

./drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c: linux/phy/phy.h is
included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Fixes: 71f68fe7 ("drm/rockchip: dsi: add ability to work as a phy instead of full dsi")
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1629454729-108701-1-git-send-email-jiapeng.chong@linux.alibaba.com