Staging: hv: mousevsc: Get rid of ref_count state in struct mousevsc_dev

Now get rid of the machinery for managing the life-cycle of the mousevsc_dev
as this is not needed.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>