drm/amd/display: add assert in enable FBC

Adding assert to prevent possible null deref warning.
Only can happen under abnormal circumstances.

Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c

@@ -1801,6 +1801,9 @@ static bool should_enable_fbc(struct dc *dc,
 		}
 	}
 
+	/* Pipe context should be found */
+	ASSERT(pipe_ctx);
+
 	/* Only supports eDP */
 	if (pipe_ctx->stream->sink->link->connector_signal != SIGNAL_TYPE_EDP)
 		return false;