mount-tool: use lowercase table column names

The "systemd-mount" tool is the one outlier in our codebase to specify
upper case column names. And it's quite pointless given that our table
output logic uppercases this anyway on output. Hence, let's fix that.

(This would be a compat break, if we'd support JSON output of this
table, but we do not currently. JSON fields use the literal column
name after all.)

src/mount/mount-tool.c

@@ -1424,7 +1424,7 @@ static int list_devices(void) {
         if (r < 0)
                 return log_error_errno(r, "Failed to add property match: %m");
 
-        table = table_new("NODE", "PATH", "MODEL", "WWN", "FSTYPE", "LABEL", "UUID");
+        table = table_new("node", "path", "model", "wwn", "fstype", "label", "uuid");
         if (!table)
                 return log_oom();