drm/exynos: fix a potential error pointer dereference

Smatch reports the warning below:
drivers/gpu/drm/exynos/exynos_hdmi.c:1864 hdmi_bind()
error: 'crtc' dereferencing possible ERR_PTR()

The return value of exynos_drm_crtc_get_by_type maybe ERR_PTR(-ENODEV),
which can not be used directly. Fix this by checking the return value
before using it.
Signed-off-by: Xiang Yang <xiangyang3@huawei.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_hdmi.c

@@ -1861,6 +1861,8 @@ static int hdmi_bind(struct device *dev, struct device *master, void *data)
 		return ret;
 
 	crtc = exynos_drm_crtc_get_by_type(drm_dev, EXYNOS_DISPLAY_TYPE_HDMI);
+	if (IS_ERR(crtc))
+		return PTR_ERR(crtc);
 	crtc->pipe_clk = &hdata->phy_clk;
 
 	ret = hdmi_create_connector(encoder);