drm/exynos: fix opencoded use of drm_panel_*

drm_panel_attach() will check if there is a controller
already attached - drop the check in the driver.

Use drm_panel_get_modes() so the driver no longer uses the function
pointer.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Kukjin Kim <kgene@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190804201637.1240-3-sam@ravnborg.org

drivers/gpu/drm/exynos/exynos_drm_dpi.c

@@ -43,7 +43,7 @@ exynos_dpi_detect(struct drm_connector *connector, bool force)
 {
 	struct exynos_dpi *ctx = connector_to_dpi(connector);
 
-	if (ctx->panel && !ctx->panel->connector)
+	if (ctx->panel)
 		drm_panel_attach(ctx->panel, &ctx->connector);
 
 	return connector_status_connected;
@@ -85,7 +85,7 @@ static int exynos_dpi_get_modes(struct drm_connector *connector)
 	}
 
 	if (ctx->panel)
-		return ctx->panel->funcs->get_modes(ctx->panel);
+		return drm_panel_get_modes(ctx->panel);
 
 	return 0;
 }