ath5k: Print stats as unsigned ints.

The debugfs code for ath5k was printing some unsigned int
stats with %d instead of %u.  This meant that you could see
negative numbers instead of a clean wrap.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>