ath9k_htc: Fix a compilation warning.

Initialize caldata to avoid compilation warning.

CC [M]  drivers/net/wireless/ath/ath9k/htc_drv_main.o
drivers/net/wireless/ath/ath9k/htc_drv_main.c: In function ‘ath9k_htc_config’:
drivers/net/wireless/ath/ath9k/htc_drv_main.c:172: warning: ‘caldata’ may be used uninitialized in this function
drivers/net/wireless/ath/ath9k/htc_drv_main.c:172: note: ‘caldata’ was declared here

Signed-off-by: Vivek Natarajan <vnatarajan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>