x86/mm: Add parenthesis for TLB tracepoint size calculation

flush_tlb_info->flush_start/end are both normal virtual
addresses.  When calculating 'nr_pages' (only used for the
tracepoint), I neglected to put parenthesis in.

Thanks to David Koufaty for pointing this out.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@sr71.net
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20150720230153.9E834081@viggo.jf.intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/tlb.c

@@ -117,7 +117,7 @@ static void flush_tlb_func(void *info)
 		} else {
 			unsigned long addr;
 			unsigned long nr_pages =
-				f->flush_end - f->flush_start / PAGE_SIZE;
+				(f->flush_end - f->flush_start) / PAGE_SIZE;
 			addr = f->flush_start;
 			while (addr < f->flush_end) {
 				__flush_tlb_single(addr);