drm/amd/display: assert if mask is 0 in set_reg_field_value_ex

-  mask = 0 means something is wrong in caller and no register field will be updated
Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dm_services.h

@@ -165,6 +165,7 @@ static inline uint32_t set_reg_field_value_ex(
 	uint32_t mask,
 	uint8_t shift)
 {
+	ASSERT(mask != 0);
 	return (reg_value & ~mask) | (mask & (value << shift));
 }