x86: Add parenthesis to IRQ vector macros

It is not good taste to have macros with additions that do not have
parenthesises around them.  This patch parethesizes the IRQ vector
macros for x86_64 arch.

Note, this caused me a bit of heart-ache debugging lguest64.

[ tglx: arch/x86 adaptation ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>