ath9k: Fix signedness in a MCI debug message

seems i got a message like this
ath: phy0: BT_Status_Update: is_link=0, linkId=2,
state=1, SEQ=-2085766476 initially.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>