wl1251: fix crash on remove due to premature kfree

Currently SDIO glue frees it's own structure before calling
wl1251_free_hw(), which in turn calls ieee80211_unregister_hw().
The later call may result in a need to communicate with the chip
to stop it (as it happens now if the interface is still up before
rmmod), which means calls are made back to the glue, resulting in
freed memory access.

Fix this by freeing glue data last.

Cc: stable@vger.kernel.org # v2.6.37+
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>