livepatch: Make 'klp_stack_entries' static

The 'klp_stack_entries' percpu array is only used in transition.c.  Make
it static.

Fixes: e92606fa

 ("livepatch: Convert stack entries array to percpu")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202305171329.i0UQ4TJa-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/5115752fca6537720700f4bf5b178959dfbca41a.1685488550.git.jpoimboe@kernel.org