init.common: give_up if usb key is in R/O mount

When running in embedded mode, the flash drive shall be in R/W mode
unless edeploy fails (no possible write to the state file or cmdb).

This occured with a read-only virtual media with the iDrac7 from Dell
but could happen also with lockable usb keys.
init: Fixing typo in unmount_embedded

The typo prevented the filesystem to be unmounted properly.