MAINTAINERS: staging: dgnc and dgap drivers: add maintainer

This patch adds the staging/dgnc [DIGI NEO AND CLASSIC
PCI PRODUCTS] and staging/dgap [DIGI EPCA PCI PRODUCTS]
drivers to the MAINTAINERS file. I am listed as the
maintainer and the driverdev-devel list is the mailing
list for these drivers.

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>