Staging: hv: Fixed FIXME comments by using list_for_each_entry

Fixed FIXME requests in channel_mgmt.c by using
list_for_each_entry.

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