ath11k: dp: clean up a variable name

The "&ar->ab->base_lock" and "&ab->base_lock" locks are the same lock
but it's nicer to use the same name consistently everywhere.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/X9s7QAHDM2OTIo3a@mwanda