Fix x86 32-bit wrong variable type for rdtsc

Bruce points out, that we are putting the result into a 32-bit
variable. That is incorrect, make it a proper ULL instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/arch/arch-x86.h b/arch/arch-x86.h
index 679ec28..8eea538 100644
--- a/arch/arch-x86.h
+++ b/arch/arch-x86.h
@@ -34,7 +34,7 @@
 
 static inline unsigned long long get_cpu_clock(void)
 {
-	unsigned long ret;
+	unsigned long long ret;
 
 	__asm__ __volatile__("rdtsc" : "=A" (ret));
 	return ret;