locking/seqlock: Fix grammar in comment

 * via WRITE_ONCE): a) to ensure the writes become visible to other threads

 * atomically, avoiding compiler optimizations; b) to document which writes are

 * meant to propagate to the reader critical section. This is necessary because

 * neither writes before and after the barrier are enclosed in a seq-writer

 * neither writes before nor after the barrier are enclosed in a seq-writer

 * critical section that would ensure readers are aware of ongoing writes::

 *

 *	seqcount_t seq;