x86, io_apic.c: Work around compiler warning

This compiler warning:

  arch/x86/kernel/apic/io_apic.c: In function ‘ioapic_write_entry’:
  arch/x86/kernel/apic/io_apic.c:466: warning: ‘eu’ is used uninitialized in this function
  arch/x86/kernel/apic/io_apic.c:465: note: ‘eu’ was declared here

Is bogus as 'eu' is always initialized. But annotate it away by
initializing the variable, to make it easier for people to notice
real warnings. A compiler that sees through this logic will
optimize away the initialization.

Signed-off-by: Figo.zhang <figo1802@gmail.com>
LKML-Reference: <1245248720.3312.27.camel@myhost>
Signed-off-by: Ingo Molnar <mingo@elte.hu>