drm/amd: fix potential memory leak

This patch fix potential memory leak (clk_src) when function run
into last return NULL.
Signed-off-by: Bernard Zhao <bernard@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn314/dcn314_resource.c

@@ -1643,6 +1643,7 @@ static struct clock_source *dcn31_clock_source_create(
 	}
 
 	BREAK_TO_DEBUGGER();
+	kfree(clk_src);
 	return NULL;
 }