time/clocksource: Fix kernel-doc warnings

Fix various KernelDoc build warnings.

Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
Cc: John Stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20111219091320.0D5AF6FC03D@msa105.auone-net.jp


Signed-off-by: Ingo Molnar <mingo@elte.hu>