hostap: Add missing annotations for prism2_bss_list_proc_start() and prism2_bss_list_proc_stop

Sparse reports warnings at prism2_bss_list_proc_start() and prism2_bss_list_proc_stop()

warning: context imbalance in prism2_wds_proc_stop() - unexpected unlock
warning: context imbalance in prism2_bss_list_proc_start() - wrong count at exit

The root cause is the missing annotations at prism2_bss_list_proc_start()

Add the missing __acquires(&local->lock) annotation
Add the missing __releases(&local->lock) annotation

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200411001933.10072-4-jbi.octave@gmail.com