drm/radeon: fix header size estimation in VM code

Only NI uses 3dw headers, SI uses 4dw headers.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/radeon_gart.c b/drivers/gpu/drm/radeon/radeon_gart.c
index 926dc9d..e9e8953 100644
--- a/drivers/gpu/drm/radeon/radeon_gart.c
+++ b/drivers/gpu/drm/radeon/radeon_gart.c
@@ -1147,17 +1147,17 @@
 
 	if (RADEON_VM_BLOCK_SIZE > 11)
 		/* reserve space for one header for every 2k dwords */
-		ndw += (nptes >> 11) * 3;
+		ndw += (nptes >> 11) * 4;
 	else
 		/* reserve space for one header for
 		    every (1 << BLOCK_SIZE) entries */
-		ndw += (nptes >> RADEON_VM_BLOCK_SIZE) * 3;
+		ndw += (nptes >> RADEON_VM_BLOCK_SIZE) * 4;
 
 	/* reserve space for pte addresses */
 	ndw += nptes * 2;
 
 	/* reserve space for one header for every 2k dwords */
-	ndw += (npdes >> 11) * 3;
+	ndw += (npdes >> 11) * 4;
 
 	/* reserve space for pde addresses */
 	ndw += npdes * 2;