x86/cpu: identify uninitialized CPU data using BAD_APICID

Uninitialized cpu_data[] entries have the apicid field set to BAD_APICID,
not boot_cpu_data.apicid.  Fix the check in cpu_smpboot_free() to use the
correct condition.

Fixes: 7126b7f806 ("x86/CPU: re-work populating of cpu_data[]")
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Teddy Astie <teddy.astie@vates.tech>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: cd0413bfac
master date: 2026-05-01 10:51:19 +0100

xen/arch/x86/smpboot.c

@@ -961,8 +961,7 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
      * In that case the socket number cannot be relied upon, but the respective
      * socket_cpumask[] slot also wouldn't have been set.
      */
-    if ( c[cpu].apicid != boot_cpu_data.apicid &&
-         cpumask_empty(socket_cpumask[socket]) )
+    if ( c[cpu].apicid != BAD_APICID && cpumask_empty(socket_cpumask[socket]) )
     {
         xfree(socket_cpumask[socket]);
         socket_cpumask[socket] = NULL;