wifi: ath9k: Remove redundant rcu_read_lock/unlock() in spin_lock

wifi: ath9k: Remove redundant rcu_read_lock/unlock() in spin_lock

Since commit a8bb74acd8efe ("rcu: Consolidate RCU-sched update-side function definitions")
there is no difference between rcu_read_lock(), rcu_read_lock_bh() and
rcu_read_lock_sched() in terms of RCU read section and the relevant grace
period. That means that spin_lock(), which implies rcu_read_lock_sched(),
also implies rcu_read_lock().

There is no need no explicitly start a RCU read section if one has already
been started implicitly by spin_lock().

Simplify the code and remove the inner rcu_read_lock() invocation.

Cc: Toke <toke@toke.dk>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: pengdonglin <pengdonglin@xiaomi.com>
Signed-off-by: pengdonglin <dolinux.peng@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20250916044735.2316171-15-dolinux.peng@gmail.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>