timekeeping: Address parameter documentation issues for various functions

The kernel-doc parser complains:

 kernel/time/timekeeping.c:1543: warning: Function parameter or member
 'ts' not described in 'read_persistent_clock64'

 kernel/time/timekeeping.c:764: warning: Function parameter or member
 'tk' not described in 'timekeeping_forward_now'

 kernel/time/timekeeping.c:1331: warning: Function parameter or member
 'ts' not described in 'timekeeping_inject_offset'

 kernel/time/timekeeping.c:1331: warning: Excess function parameter 'tv'
 description in 'timekeeping_inject_offset'

Add the missing parameter documentations and rename the 'tv' parameter of
timekeeping_inject_offset() to 'ts' so it matches the implemention.

[ tglx: Reworded a few docs and 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/1605252275-63652-5-git-send-email-alex.shi@linux.alibaba.com