locking/qspinlock: Clarify pending field layout

For CONFIG_NR_CPUS < 16K, _Q_PENDING_BITS is 8 and the pending
field occupies bits 8-15 of the lock word. The current comment
documents bit 8 as pending and bits 9-15 as unused, which describes
the pending flag value rather than the field layout.

Describe bits 8-15 as the pending byte so the layout description
is consistent with the lock byte.

Signed-off-by: WEI-HONG, YE <1234567weewee457@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://patch.msgid.link/20260525130450.723937-1-1234567weewee457@gmail.com

include/asm-generic/qspinlock_types.h

@@ -53,8 +53,7 @@ typedef struct qspinlock {
  *
  * When NR_CPUS < 16K
  *  0- 7: locked byte
- *     8: pending
- *  9-15: not used
+ *  8-15: pending byte
  * 16-17: tail index
  * 18-31: tail cpu (+1)
  *