x86/its: Fix an ifdef typo in its_alloc()

Commit a82b2645 ("x86/its: explicitly manage permissions for ITS
pages") reworks its_alloc() and introduces a typo in an ifdef
conditional, referring to CONFIG_MODULE instead of CONFIG_MODULES.

Fix this typo in its_alloc().

Fixes: a82b2645 ("x86/its: explicitly manage permissions for ITS pages")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20250616100432.22941-1-lukas.bulwahn%40redhat.com