ath5k: remove ath5k_hw_get_capability(), don't use VEOL on AR5210

There are only two capabilities we need, and both are trivial to find.

ath5k_hw_hasbssidmask() is true on AR5212, but not on AR5210 or AR5211.

ath5k_hw_hasveol() is true on AR5211 and AR5212, but not on AR5210,
according to the HAL source.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>