MAINTAINERS: ieee802154: update documentation file pattern

When moving the documentation for the ieee802154 subsystem from
plain text to rst the file pattern in the MAINTAINERS file got wrong.
Updating it here to fix scripts using this file.

Reported-by: Joe Perches <[email protected]>
Signed-off-by: Stefan Schmidt <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Stefan-Schmidt

MAINTAINERS

@@ -7515,7 +7515,7 @@ F:	include/net/mac802154.h
 F:	include/net/af_ieee802154.h
 F:	include/net/cfg802154.h
 F:	include/net/ieee802154_netdev.h
-F:	Documentation/networking/ieee802154.txt
+F:	Documentation/networking/ieee802154.rst
 
 IFE PROTOCOL
 M:	Yotam Gigi <[email protected]>