MAINAINERS: Add details for drivers/staging/et131x

Adding myself as a maintainer for this driver, as I appear to have been the only interested party for some time.
Not sure if Olaf Hartman is still interested? So will leave it up to him to add his name to the list.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

MAINTAINERS

@@ -6172,6 +6172,11 @@ M:	David Rowe <david@rowetel.com>
 S:	Odd Fixes
 F:	drivers/staging/echo/
 
+STAGING - ET131X NETWORK DRIVER
+M:	Mark Einon <mark.einon@gmail.com>
+S:	Odd Fixes
+F:	drivers/staging/et131x/
+
 STAGING - FLARION FT1000 DRIVERS
 M:	Marek Belisko <marek.belisko@gmail.com>
 S:	Odd Fixes