docs: i2c: Fix SPDX-License-Identifier syntax

ReST directives are introduced with two dots.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/i2c/index.rst b/Documentation/i2c/index.rst
index cd8d020..a0fbaf6 100644
--- a/Documentation/i2c/index.rst
+++ b/Documentation/i2c/index.rst
@@ -1,4 +1,4 @@
-. SPDX-License-Identifier: GPL-2.0
+.. SPDX-License-Identifier: GPL-2.0
 
 ===================
 I2C/SMBus Subsystem