Do not try to enable btrfs compression

This is just a warning for others who like me may think it’s a great idea to enable compression on the btrfs filesystem in order to “save” flash: your Omnia is likely to become unbootable, since the u-boot bootloader cannot handle compression and won’t be able to load the kernel from the filesystem. (I had to use the serial cable in order to find out, then rolled back to a previous snapshot.)