drm/tegra: dsi - Fix typo when disabling controller

When disabling the DSI controller, the code wasn't really doing what it
was supposed to.

Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/drivers/gpu/drm/tegra/dsi.c b/drivers/gpu/drm/tegra/dsi.c
index 4c35d9b..55ac86f 100644
--- a/drivers/gpu/drm/tegra/dsi.c
+++ b/drivers/gpu/drm/tegra/dsi.c
@@ -550,7 +550,7 @@
 
 	/* disable DSI controller */
 	value = tegra_dsi_readl(dsi, DSI_POWER_CONTROL);
-	value &= DSI_POWER_CONTROL_ENABLE;
+	value &= ~DSI_POWER_CONTROL_ENABLE;
 	tegra_dsi_writel(dsi, value, DSI_POWER_CONTROL);
 
 	/*