mkfs.ubifs: fix regression when trying to store device special files

mkfs.ubifs: fix regression when trying to store device special files

Commit a767dd30 added a check to add_inode that bails when trying to
store extra data in anything other than a symlink. The symlink
encryption support added by that commit relies on the assumption.

Unfortionately it was overlooked that device special files also store
the device number as additional data in the inode. The check added in
commit a767dd30 broke support for device files in mkfs.ubifs.

This commit adds a quick and dirty fix, moving the check into the
fscrypt branch, breaking only the fscrypt version but restoring old
functionality for unencrypted file systems.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>