staging: unisys: Add checks for creation

There was a bunch of channel creation checks before the
visorchannel_create function was called, moving some of those
checks inside.  This keeps the outside code cleaner and handles
the situation where a caller forgets to make these checks.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>