hyper-v: Update MAINTAINERS

Update the MAINTAINERS file to reflect the current state
of the Hyper-V drivers.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>