mwifiex: avoid -Wstringop-overflow warning

gcc-10 reports a warning for mwifiex_cmd_802_11_key_material_v1:

drivers/net/wireless/marvell/mwifiex/sta_cmd.c: In function 'mwifiex_cmd_802_11_key_material_v1':
cc1: warning: writing 16 bytes into a region of size 0 [-Wstringop-overflow=]
In file included from drivers/net/wireless/marvell/mwifiex/sta_cmd.c:23:
drivers/net/wireless/marvell/mwifiex/fw.h:993:9: note: at offset 0 to object 'action' with size 2 declared here
  993 |  __le16 action;
      |         ^~~~~~

As the warning makes no sense, I reported it as a bug for gcc. In the
meantime using a temporary pointer for the key data makes the code easier
to read and stops the warning.

Fixes: 5e6e3a92 ("wireless: mwifiex: initial commit for Marvell mwifiex driver")
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94881


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200430213101.135134-4-arnd@arndb.de