firmware: vpd: use memunmap instead of iounmap

In functions vpd_sections_init() and vpd_section_init(), iounmap() is
used to unmap memory. However, in these cases, memunmap() should be
used.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>