genirq: Use scoped_guard() to shut clang up

This code pattern trips clang up:

     if (fail)
     	goto undo;

     guard(lock)(lock);
     do_stuff();
     return 0;

undo:
     ...

as it somehow extends the scope of the guard beyond the return statement.

Replace it with a scoped guard to help it to get its act together.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Closes: https://lore.kernel.org/oe-kbuild-all/202505071809.ajpPxfoZ-lkp@intel.com/