ath6kl: fix enum-conversion warning

gcc -Wextra points out a type mismatch

drivers/net/wireless/ath/ath6kl/wmi.c: In function 'ath6kl_wmi_cmd_send':
drivers/net/wireless/ath/ath6kl/wmi.c:1825:19: warning: implicit conversion from 'enum <anonymous>' to 'enum wmi_data_hdr_data_type' [-Wenum-conversion]
 1825 |            false, false, 0, NULL, if_idx);
      |                   ^~~~~

As far as I can tell, the numeric value is current here,
so just use the correct enum literal instead of 'false'.

Fixes: bdcd8170 ("Add ath6kl cleaned up driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201026213040.3889546-9-arnd@kernel.org