ath9k: simplify btcoex profile management

This patch simplifies profile management utility functions.

* Separate find_profile from add/del functions
* Return correct values when the profile list is empty or
  profile is ot found
* flush the profiles when there are entries in the list

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