ath5k: Fix lockup due to un-init spinlock.

This was introduced in 2.6.39-rc1 it seems.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Tested-by: Sedat Dilek <sedat.dilek@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>