drm/radeon/dpm: disable sclk ss on rv6xx

Enabling spread spectrum on the engine clock
leads to hangs on some asics.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=66963

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/rv6xx_dpm.c

@@ -1992,6 +1992,9 @@ int rv6xx_dpm_init(struct radeon_device *rdev)
 	pi->mclk_ss = radeon_atombios_get_asic_ss_info(rdev, &ss,
 						       ASIC_INTERNAL_MEMORY_SS, 0);
 
+	/* Disable sclk ss, causes hangs on a lot of systems */
+	pi->sclk_ss = false;
+
 	if (pi->sclk_ss || pi->mclk_ss)
 		pi->dynamic_ss = true;
 	else