zfs-mount-genrator: dependencies should be space-separated

Reviewed-by: Antonio Russo <antonio.e.russo@gmail.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Closes #9174

etc/systemd/system-generators/zfs-mount-generator.in

@@ -215,7 +215,7 @@ EOF
     fi
     # Update the dependencies for the mount file to require the
     # key-loading unit.
-    wants="${wants},${keyloadunit}"
+    wants="${wants} ${keyloadunit}"
   fi
 
   # If the mountpoint has already been created, give it precedence.