Fix Plymouth passphrase prompt in initramfs script

Fix Plymouth passphrase prompt in initramfs script

Entering the ZFS encryption passphrase under Plymouth wasn't working
because in the ZFS initrd script, Plymouth was calling zfs via
"--command", which wasn't passing through the filesystem argument to
zfs load-key properly (it was passing through the single quotes around
the filesystem name intended to handle spaces literally,
which zfs load-key couldn't understand).

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Garrett Fields <ghfields@gmail.com>
Signed-off-by: Richard Allen <belperite@gmail.com>
Issue #9193
Closes #9202