dt-bindings: Fix .gitignore

The tracked files should not be ignored.

Fixes: 44ec8b20 ("dt-bindings: Add running yamllint to dt_binding_check")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230127150225.18148-1-andriy.shevchenko@linux.intel.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/.gitignore

@@ -2,3 +2,8 @@
 *.example.dts
 /processed-schema*.yaml
 /processed-schema*.json
+
+#
+# We don't want to ignore the following even if they are dot-files
+#
+!.yamllint