Staging: hv: remove gDriver variable

It's only set and never used anymore, so remove it.

Gotta love static variables with a "global" hungarian notatation on the
name...

Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>