ath6kl: get rid of AR_DBG_LVL_CHECK()

We don't need it as debug calls already have a log level and compiler
should be smart enough to optimise away the code when ath6kl debug code
is not enabled. Also it makes it easier to abstract core code to
ath6kl_core.ko.

In ath6kl_dump_registers() I had to change the debug level from ANY to IRQ
as I removed the AR_DBG_LVL_CHECK() check before calling the function.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>