x86/cet: Use symbolic name for #CP

Make use of the symbolic name for the #CP vector number instead of
hard-coding its value.

Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230413184219.36404-5-minipli@grsecurity.net
Signed-off-by: Sean Christopherson <seanjc@google.com>

x86/cet.c

@@ -83,7 +83,7 @@ int main(int ac, char **av)
 	}
 
 	setup_vm();
-	handle_exception(21, handle_cp);
+	handle_exception(CP_VECTOR, handle_cp);
 
 	/* Allocate one page for shadow-stack. */
 	shstk_virt = alloc_vpage();