cmdgen: fix a tiny memory leak.

One of those things you'd never notice if it weren't for Leak
Sanitiser happening to be turned on while you were doing something
else: freersakey() frees all the things pointed to _from_ an RSAKey
structure, but not the structure itself.

cmdgen.c

@@ -1076,6 +1076,7 @@ int main(int argc, char **argv)
 
     if (ssh1key) {
 	freersakey(ssh1key);
+        sfree(ssh1key);
     }
     if (ssh2key) {
 	sfree(ssh2key->comment);