drm/amd/display: remove redundant null pointer check before kfree

kfree has taken null pointer into account. hence it is safe to remove
the unnecessary check.

Reviewed-by: Harry Wentland <[email protected]>
Signed-off-by: zhong jiang <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: xiongzhongjiang

drivers/gpu/drm/amd/display/dc/hdcp/hdcp_msg.c

@@ -174,9 +174,7 @@ static bool hdmi_14_process_transaction(
 			link->ctx,
 			link,
 			&i2c_command);
-
-	if (buff)
-		kfree(buff);
+	kfree(buff);
 
 	return result;
 }