Staging: hv: Remove check for NULL before calling kfree()

kfree() knows how to deal with NULL, so there's no reason to check for
NULL before passing something to it.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>