sata_highbank: clear whole array in highbank_initialize_phys()

The original code used the wrong parameter to clear tx_atten[].  It
passed the number of elements instead of sizeof() the array to memset.

The other potential issue was that cphy_base[] wasn't cleared.  I'm not
sure if that was a real problem or not, but I have cleared it in my
patch.

Instead of using memset(), this patch uses empty initializers as a
cleanup.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Tejun Heo <tj@kernel.org>