MAINTAINERS: Add .clang-format entry

As discussed in https://lkml.org/lkml/2018/6/25/877Signed-off-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>

MAINTAINERS

@@ -3514,6 +3514,11 @@ M:	Dave Goodell <dgoodell@cisco.com>
 S:	Supported
 F:	drivers/infiniband/hw/usnic/
 
+CLANG-FORMAT FILE
+M:	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
+S:	Maintained
+F:	.clang-format
+
 CLEANCACHE API
 M:	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 L:	linux-kernel@vger.kernel.org