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>

drivers/net/ethernet/faraday/ftgmac100.c

@@ -1835,7 +1835,7 @@ static int ftgmac100_probe(struct platform_device *pdev)
 		}
 
 		/* Indicate that we support PAUSE frames (see comment in
-		 * Documentation/networking/phy.txt)
+		 * Documentation/networking/phy.rst)
 		 */
 		phy_support_asym_pause(phy);