ath5k: improve pcal error handling for ENOMEM case

The ath5k driver does kmalloc allocations for pcal info in a loop.
But, if one fails it was simply returning -ENOMEM without freeing
already allocated memory.  This patch corrects that oversight.

Reported-by: Eugene A. Shatokhin <dame_eugene@mail.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Reviewed-by: Bob Copeland <me@bobcopeland.com>