video: rockchip: dw_mipi_dsi: Fix external phy existence check

&priv->phy is always true. Compiler warns about this loudly.

Use a propper check for phy device allocation. Without this fix
using this driver with SoC that doesn't use external phy (eg. RK3399)
doesn't work.

Signed-off-by: Ondrej Jirman <megi@xff.cz>
diff --git a/drivers/video/rockchip/dw_mipi_dsi_rockchip.c b/drivers/video/rockchip/dw_mipi_dsi_rockchip.c
index ca548a6..b1b5328 100644
--- a/drivers/video/rockchip/dw_mipi_dsi_rockchip.c
+++ b/drivers/video/rockchip/dw_mipi_dsi_rockchip.c
@@ -344,7 +344,7 @@
 	struct dw_rockchip_dsi_priv *dsi = dev_get_priv(dev);
 	int ret, i, vco;
 
-	if (&dsi->phy) {
+	if (dsi->phy.dev) {
 		ret = generic_phy_configure(&dsi->phy, &dsi->phy_opts);
 		if (ret) {
 			dev_err(dsi->dsi_host,
@@ -527,7 +527,7 @@
 	}
 
 	/* for external phy only the mipi_dphy_config is necessary */
-	if (&dsi->phy) {
+	if (dsi->phy.dev) {
 		phy_mipi_dphy_get_default_config(timings->pixelclock.typ  * 10 / 8,
 						 bpp, lanes,
 						 &dsi->phy_opts);
@@ -827,7 +827,7 @@
 	}
 
 	/* Get a ref clock only if not using an external phy. */
-	if (&priv->phy) {
+	if (priv->phy.dev) {
 		dev_dbg(dev, "setting priv->ref to NULL\n");
 		priv->ref = NULL;