timekeeping: Fix parameter docs of read_persistent_wall_and_boot_offset()

Address the following kernel-doc markup warnings:

 kernel/time/timekeeping.c:1563: warning: Function parameter or member
 'wall_time' not described in 'read_persistent_wall_and_boot_offset'
 kernel/time/timekeeping.c:1563: warning: Function parameter or member
 'boot_offset' not described in 'read_persistent_wall_and_boot_offset'

The parameters are described but miss the leading '@' and the colon after
the parameter names.

[ tglx: Massaged changelog ]
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/1605252275-63652-6-git-send-email-alex.shi@linux.alibaba.com

kernel/time/timekeeping.c

@@ -1576,8 +1576,9 @@ void __weak read_persistent_clock64(struct timespec64 *ts)
  *                                        from the boot.
  *
  * Weak dummy function for arches that do not yet support it.
- * wall_time	- current time as returned by persistent clock
- * boot_offset	- offset that is defined as wall_time - boot_time
+ * @wall_time:	- current time as returned by persistent clock
+ * @boot_offset: - offset that is defined as wall_time - boot_time
+ *
  * The default function calculates offset based on the current value of
  * local_clock(). This way architectures that support sched_clock() but don't
  * support dedicated boot time clock will provide the best estimate of the