drm/amd/display: Make sure line size is not zero in DCN2 line buffer size calculations

[why]
'Divide by zero' error happens when line size happens to be zero.

[how]
The code that makes sure line size minimum value can be 1 was already
present in DCN1 part of the driver, this is mearly a port to DCN2.
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_dpp.c

@@ -251,14 +251,23 @@ void dscl2_calc_lb_num_partitions(
 		int *num_part_y,
 		int *num_part_c)
 {
+	int memory_line_size_y, memory_line_size_c, memory_line_size_a,
+	lb_memory_size, lb_memory_size_c, lb_memory_size_a, num_partitions_a;
+
 	int line_size = scl_data->viewport.width < scl_data->recout.width ?
 			scl_data->viewport.width : scl_data->recout.width;
 	int line_size_c = scl_data->viewport_c.width < scl_data->recout.width ?
 			scl_data->viewport_c.width : scl_data->recout.width;
-	int memory_line_size_y = (line_size + 5) / 6; /* +5 to ceil */
-	int memory_line_size_c = (line_size_c + 5) / 6; /* +5 to ceil */
-	int memory_line_size_a = (line_size + 5) / 6; /* +5 to ceil */
-	int lb_memory_size, lb_memory_size_c, lb_memory_size_a, num_partitions_a;
+
+	if (line_size == 0)
+		line_size = 1;
+
+	if (line_size_c == 0)
+		line_size_c = 1;
+
+	memory_line_size_y = (line_size + 5) / 6; /* +5 to ceil */
+	memory_line_size_c = (line_size_c + 5) / 6; /* +5 to ceil */
+	memory_line_size_a = (line_size + 5) / 6; /* +5 to ceil */
 
 	if (lb_config == LB_MEMORY_CONFIG_1) {
 		lb_memory_size = 970;