drm/etnaviv: Fix error path on failure to enable bus clk

Since commit 65f037e8 ("drm/etnaviv: add support for slave interface
clock") the reg clock is enabled before the bus clock and we need to undo
its enablement on error.

Fixes: 65f037e8 ("drm/etnaviv: add support for slave interface clock")
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_gpu.c

@@ -1496,7 +1496,7 @@ static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
 	if (gpu->clk_bus) {
 		ret = clk_prepare_enable(gpu->clk_bus);
 		if (ret)
-			return ret;
+			goto disable_clk_reg;
 	}
 
 	if (gpu->clk_core) {
@@ -1519,6 +1519,9 @@ static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
 disable_clk_bus:
 	if (gpu->clk_bus)
 		clk_disable_unprepare(gpu->clk_bus);
+disable_clk_reg:
+	if (gpu->clk_reg)
+		clk_disable_unprepare(gpu->clk_reg);
 
 	return ret;
 }