Assemble: ignore unknown devices not listed on command line.

If we find a device that has not superblock, we currently fail
unless in auto_assem mode.
However we really should only fail if the device was explicitly listed
in the arg list.  So add a test for that.

Signed-off-by: NeilBrown <neilb@suse.de>

Assemble.c

@@ -379,7 +379,7 @@ int Assemble(struct supertype *st, char *mddev,
 		}
 		if (dfd >= 0) close(dfd);
 		if (tmpdev->used == 2) {
-			if (auto_assem)
+			if (auto_assem || !inargv)
 				/* Ignore unrecognised devices during auto-assembly */
 				goto loop;
 			if (ident->uuid_set || ident->name[0] ||