x86/apic/32: Fix yet another implicit fallthrough warning

Fix

  arch/x86/kernel/apic/probe_32.c: In function ‘default_setup_apic_routing’:
  arch/x86/kernel/apic/probe_32.c:146:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
      if (!APIC_XAPIC(version)) {
         ^
  arch/x86/kernel/apic/probe_32.c:151:3: note: here
   case X86_VENDOR_HYGON:
   ^~~~

for 32-bit builds.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190811154036.29805-1-bp@alien8.de