MAINTAINERS: add patterns to DELL WMI EXTRAS

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>