vdso/datapage: Use correct clock mode name in comment

While the explanation for time namespace <-> vdso interactions is very
helpful it uses the wrong name in the comment when describing the clock
mode making grepping a bit annoying.

This seems like an accidental oversight when moving from VCLOCK_TIMENS
to VDSO_CLOCKMODE_TIMENS. It seems that
660fd04 ("lib/vdso: Prepare for time namespace support") misspelled
VCLOCK_TIMENS as VLOCK_TIMENS which explains why it got missed when
VCLOCK_TIMENS became VDSO_CLOCKMODE_TIMENS in
2d6b01b ("lib/vdso: Move VCLOCK_TIMENS to vdso_clock_modes").

Update the comment to use VDSO_CLOCKMODE_TIMENS.

Fixes: 660fd04 ("lib/vdso: Prepare for time namespace support")
Fixes: 2d6b01b ("lib/vdso: Move VCLOCK_TIMENS to vdso_clock_modes")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andrei Vagin <avagin@gmail.com>
Acked-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lkml.kernel.org/r/20200420100615.1549804-1-christian.brauner@ubuntu.com

include/vdso/datapage.h

@@ -73,8 +73,8 @@ struct vdso_timestamp {
  *
  * @offset is used by the special time namespace VVAR pages which are
  * installed instead of the real VVAR page. These namespace pages must set
- * @seq to 1 and @clock_mode to VLOCK_TIMENS to force the code into the
- * time namespace slow path. The namespace aware functions retrieve the
+ * @seq to 1 and @clock_mode to VDSO_CLOCKMODE_TIMENS to force the code into
+ * the time namespace slow path. The namespace aware functions retrieve the
  * real system wide VVAR page, read host time and add the per clock offset.
  * For clocks which are not affected by time namespace adjustment the
  * offset must be zero.