x86: pageattr.c fix shadowed variable warning

irqs_disabled() uses flags internally, use _flags to avoid shadowing
code calling into this macro.

Introduced between 2.6.25-rc3 and -rc4

Fixes the sparse warning:
arch/x86/mm/pageattr.c:383:21: warning: symbol 'flags' shadows an earlier one
arch/x86/mm/pageattr.c:369:16: originally declared here

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>