Staging: hv: netvsc_drv: Make netvsc_drv an instance of struct hv_driver

In preparation to getting rid of struct  netvsc_driver, make
the variable netvsc_drv an instance of struct hv_driver.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>