ar9170: fix bug in iq-auto calibration value calculation

This patch fixes a embarrassing bug which was introduced by:
"[PATCH] ar9170: implement frequency calibration for one-stage/openfw"

The phy_data variable initialization has to done outside the for-loop
scope. This is because the for-loop uses u32 phy_data variable more
like a 4-byte field. But in each run only a single byte is calculated.
Therefore phy_data content needs to stay the same for at least 3 more
iterations, before the complete set can be uploaded.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>