timekeeping: Fix parameter docs of read_persistent_wall_and_boot_offset()

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