fix hf mfu pwdgen for 7 byte uid

The last 3 bytes of the 7 byte uid are zeroed out
Tested with the example from the forum http://www.proxmark.org/forum/viewtopic.php?pid=44238#p44238

Signed-off-by: Anton Todorov <ANTodorov@users.noreply.github.com>

client/src/cmdhfmfu.c

@@ -4392,10 +4392,6 @@ static int CmdHF14AMfUPwdGen(const char *Cmd) {
         if (u_len != 7 && u_len != 4) {
             PrintAndLogEx(WARNING, "Key must be 7 hex bytes");
             return PM3_EINVARG;
-        } else {
-            // adapt to 7 bytes :)
-            memset(uid + 4, 0x00, 3);
-            u_len = 7;
         }
     }