locking/pvqspinlock: Correct the type of "old" variable in pv_kick_node()

"enum vcpu_state" is not compatible with "u8" type for all targets,
resulting in:

error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *'

for LoongArch. Correct the type of "old" variable to "u8".

Fixes: fea0e182 ("locking/pvqspinlock: Use try_cmpxchg() in qspinlock_paravirt.h")
Closes: https://lore.kernel.org/lkml/20240719024010.3296488-1-maobibo@loongson.cn/


Reported-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20240721164552.50175-1-ubizjak@gmail.com