wil6210: fix access after free in wil_pcie_remove()

'wil'  released in wil_if_free(); save iomapped address aside to
properly unmap it.

Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>