wifi: ath9k: work around memset overflow warning

wifi: ath9k: work around memset overflow warning

gcc-9 and some other older versions produce a false-positive warning
for zeroing two fields

In file included from include/linux/string.h:369,
                 from drivers/net/wireless/ath/ath9k/main.c:18:
In function 'fortify_memset_chk',
    inlined from 'ath9k_ps_wakeup' at drivers/net/wireless/ath/ath9k/main.c:140:3:
include/linux/fortify-string.h:462:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  462 |                         __write_overflow_field(p_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Using a struct_group seems to reliably avoid the warning and
not make the code much uglier. The combined memset() should even
save a couple of cpu cycles.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240328135509.3755090-3-arnd@kernel.org