exec/ioport: Resolve redundant .base attribute in struct MemoryRegionPortio

exec/ioport: Resolve redundant .base attribute in struct MemoryRegionPortio

portio_list_add_1() creates a MemoryRegionPortioList instance which holds a
MemoryRegion `mr` and an array of MemoryRegionPortio elements named `ports`.
Each element in the array gets assigned the same value for its .base attribute.
The same value also ends up as the .addr attribute of `mr` due to the
memory_region_add_subregion() call. This means that all .base attributes are
the same as `mr.addr`.

The only usages of MemoryRegionPortio::base were in portio_read() and
portio_write(). Both functions get above MemoryRegionPortioList as their
opaque parameter. In both cases find_portio() can only return one of the
MemoryRegionPortio elements of the `ports` array. Due to above observation any
element will have the same .base value equal to `mr.addr` which is also
accessible.

Hence, `mrpio->mr.addr` is equivalent to `mrp->base` and
MemoryRegionPortio::base is redundant and can be removed.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Message-Id: <20240114123911.4877-5-shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>