plugins: Fix physical address calculation for IO regions

The address calculation for IO regions introduced by

commit 787148bf92
Author: Aaron Lindsay <aaron@os.amperecomputing.com>
    plugins: Expose physical addresses instead of device offsets

is not always accurate. Use the more correct
MemoryRegionSection.offset_within_address_space.

Signed-off-by: Aaron Lindsay <aaron@os.amperecomputing.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210720195735.3934473-1-aaron@os.amperecomputing.com>
Message-Id: <20210720232703.10650-25-alex.bennee@linaro.org>

plugins/api.c

@@ -319,7 +319,7 @@ uint64_t qemu_plugin_hwaddr_phys_addr(const struct qemu_plugin_hwaddr *haddr)
             return block->offset + offset + block->mr->addr;
         } else {
             MemoryRegionSection *mrs = haddr->v.io.section;
-            return haddr->v.io.offset + mrs->mr->addr;
+            return mrs->offset_within_address_space + haddr->v.io.offset;
         }
     }
 #endif