s390/vdso: simplify __arch_get_hw_counter()

Use the passed in vdso_data pointer instead of calculating it again.
This is also required as a prerequisite for vdso time namespaces: if a
process is part of a time namespace __arch_get_vdso_data() will return
a pointer to the time namespace data page instead of the vdso data
page, which is not what __arch_get_hw_counter() expects.
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/vdso/gettimeofday.h

@@ -24,13 +24,12 @@ static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
 
 static inline u64 __arch_get_hw_counter(s32 clock_mode, const struct vdso_data *vd)
 {
-	const struct vdso_data *vdso = __arch_get_vdso_data();
 	u64 adj, now;
 
 	now = get_tod_clock();
-	adj = vdso->arch_data.tod_steering_end - now;
+	adj = vd->arch_data.tod_steering_end - now;
 	if (unlikely((s64) adj > 0))
-		now += (vdso->arch_data.tod_steering_delta < 0) ? (adj >> 15) : -(adj >> 15);
+		now += (vd->arch_data.tod_steering_delta < 0) ? (adj >> 15) : -(adj >> 15);
 	return now;
 }