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>

drivers/staging/unisys/visorbus/visorchannel.c

@@ -62,6 +62,9 @@ visorchannel_create_guts(u64 physaddr, unsigned long channel_bytes,
 	int err;
 	size_t size = sizeof(struct channel_header);
 
+	if (physaddr == 0)
+		return NULL;
+
 	channel = kzalloc(sizeof(*channel), gfp);
 	if (!channel)
 		goto cleanup;