cryptsetup: fix unitialized variable

CID #1368416.

Coverity web interface is back, yay!

src/cryptsetup/cryptsetup.c

@@ -750,6 +750,7 @@ int main(int argc, char *argv[]) {
 
         } else {
                 log_error("Unknown verb %s.", argv[1]);
+                r = -EINVAL;
                 goto finish;
         }