notifier: repair slips in kernel-doc comments

Invoking ./scripts/kernel-doc -none kernel/notifier.c warns:

  kernel/notifier.c:71: warning: Excess function parameter 'returns' description in 'notifier_call_chain'
  kernel/notifier.c:119: warning: Function parameter or member 'v' not described in 'notifier_call_chain_robust'

These two warning are easy to fix, as they are just due to some minor slips
that makes the comment not follow kernel-doc's syntactic expectation.

Fix those minor slips in kernel-doc comments for make W=1 happiness.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>