ath9k: Fix BTCOEX debugfs file usage

The debugfs file for dumping btcoex parameters unconditionally
assumes a MCI-based device. This will not work for older btcoex
chips. Fix this by branching out the routine into separate
functions.

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