pvclock: Get rid of __pvclock_read_cycles in function pvclock_read_flags

There is a generic function __pvclock_read_cycles to be used to get both
flags and cycles. For function pvclock_read_flags, it's useless to get
cycles value. To make this function be more effective, get this variable
flags directly in function.
Signed-off-by: NMinfei Huang <mnghuan@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kernel/pvclock.c

@@ -61,11 +61,14 @@ void pvclock_resume(void)
 u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
 {
 	unsigned version;
-	cycle_t ret;
 	u8 flags;
 
 	do {
-		version = __pvclock_read_cycles(src, &ret, &flags);
+		version = src->version;
+		/* Make the latest version visible */
+		smp_rmb();
+
+		flags = src->flags;
 		/* Make sure that the version double-check is last. */
 		smp_rmb();
 	} while ((src->version & 1) || version != src->version);