ath9k_htc: Fix WMI command race

My patch "ath9k_htc: Handle WMI timeouts properly" introduced
a race condition in WMI command processing. The last issued command
should be stored _before_ issuing a WMI command. Not doing this
would result in the WMI event IRQ dropping correct command responses
as invalid.

Fix this race by storing the command id correctly.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>