UBI: gluebi: initialize ubi_num field

Do not forget to initialize 'gluebi->ubi_num' because otherwise
it will stay 0 even for ubi1 device, and gluebi will open
wrong UBI device when 'gluebi_get_device()' is called.

Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/gluebi.c

···
 	}
 
 	gluebi->vol_id = vi->vol_id;
+	gluebi->ubi_num = vi->ubi_num;
 	mtd->type = MTD_UBIVOLUME;
 	if (!di->ro_mode)
 		mtd->flags = MTD_WRITEABLE;