x86, cleanup: Remove obsolete boot_cpu_id variable

boot_cpu_id is there for historical reasons and was renamed to
boot_cpu_physical_apicid in patch:

 c70dcb7 x86: change boot_cpu_id to boot_cpu_physical_apicid

However, there are some remaining occurrences of boot_cpu_id that are
never touched in the kernel and thus its value is always 0.

This patch removes boot_cpu_id completely.

Signed-off-by: Robert Richter <robert.richter@amd.com>
LKML-Reference: <1279731838-1522-8-git-send-email-robert.richter@amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index a60df9a..2335c15 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -253,7 +253,7 @@
 		 * Up to this point, the boot CPU has been using .init.data
 		 * area.  Reload any changed state for the boot CPU.
 		 */
-		if (cpu == boot_cpu_id)
+		if (!cpu)
 			switch_to_new_gdt(cpu);
 	}