fit-image.its: ramdisk compression should always be set to none

The decompression of the ramdisk is always done by the kernel
rather than u-boot. With this change the following warning is
no longer seen.

WARNING: 'compression' nodes for ramdisks are deprecated,
please fix your .its file!

See u-boot commit bddd985734653c366c8da073650930fb2e9b5003 for
the introduction of the warning and justification for always
setting ramdisk compression to none.

Also, remove a stray tab.

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Change-Id: Ie44d717693917fe714c42b7bb7d0fa6f96d72060