drm/i915/display: Avoid divide by zero

skl_crtc_allocate_plane_ddb allow iter.data_rate to be zero
which could cause divide by zero in skl_allocate_plane_ddb,
check against that.

Signed-off-by: Juha-Pekka Heikkila <[e-mail]>
Reviewed-by: Suraj Kandpal <[e-mail]>
Signed-off-by: Mika Kahola <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/i915/display/skl_watermark.c

···
 {
 	u16 size, extra = 0;
 
-	if (data_rate) {
+	if (data_rate && iter->data_rate) {
 		extra = min_t(u16, iter->size,
 			      DIV64_U64_ROUND_UP(iter->size * data_rate,
 						 iter->data_rate));