drm/radeon/ss: use num_crtc rather than hardcoded 6

When checking if a pll is in use.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c
index cb18813..f4d4505 100644
--- a/drivers/gpu/drm/radeon/atombios_crtc.c
+++ b/drivers/gpu/drm/radeon/atombios_crtc.c
@@ -452,7 +452,7 @@
 	union atom_enable_ss args;
 
 	if (!enable) {
-		for (i = 0; i < 6; i++) {
+		for (i = 0; i < rdev->num_crtc; i++) {
 			if (rdev->mode_info.crtcs[i] &&
 			    rdev->mode_info.crtcs[i]->enabled &&
 			    i != crtc_id &&