ath9k: ar9002_mac: kill off ACCESS_ONCE()

For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't currently harmful.

However, for some new features (e.g. KTSAN / Kernel Thread Sanitizer),
it is necessary to instrument reads and writes separately, which is not
possible with ACCESS_ONCE(). This distinction is critical to correct
operation.

It's possible to transform the bulk of kernel code using the Coccinelle
script below. However, for some files (including the ath9k ar9002 mac
driver), this mangles the formatting. As a preparatory step, this patch
converts the driver to use {READ,WRITE}_ONCE() without said mangling.

----
virtual patch

@ depends on patch @
expression E1, E2;
@@

- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)

@ depends on patch @
expression E;
@@

- ACCESS_ONCE(E)
+ READ_ONCE(E)
----

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: ath9k-devel@qca.qualcomm.com
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: linux-wireless@vger.kernel.org
Cc: ath9k-devel@lists.ath9k.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>