Staging: hv: mousevsc: Fixup some bogus WARN_ON() calls

Fix the bogus WARN_ON() calls.

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>