docs: fix some broken references

There are a number of documentation files that got moved or
renamed. update their references.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Shannon Nelson <snelson@pensando.io>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Paul Walmsley <paul.walmsley@sifive.com> # RISC-V
Acked-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/MAINTAINERS b/MAINTAINERS
index b20bc42..7c81417 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3683,7 +3683,7 @@
 R:	Pengutronix Kernel Team <kernel@pengutronix.de>
 L:	linux-can@vger.kernel.org
 S:	Maintained
-F:	Documentation/networking/j1939.txt
+F:	Documentation/networking/j1939.rst
 F:	net/can/j1939/
 F:	include/uapi/linux/can/j1939.h