Staging: hv: warn the world of a bug in the release function

All device release functions need to do something, if not, it's a bug.
By merely providing an "empty" release function, it gets the kernel to
shut up, but that's not solving the problem at all.  Stick a big fat
WARN_ON(1); in there to get people's attention.

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