rtlwifi: btcoexist: avoid format string in printk

Recent changes to this driver inadvertently reverted the change made by Kees
Cook in commit 6437f51e.

Reported-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>