Show length mismatch error is hex

When live migrate fails due to a section length mismatch we currently
see an error message like:

Length mismatch: 0000:00:03.0/virtio-net-pci.rom: 10000 in != 20000

The section lengths are in fact in hex, so this should read

Length mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x10000 in != 0x20000

Correct the error string to reflect this.
Signed-off-by: NAlex Bligh <alex@alex.org.uk>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

arch_init.c

@@ -1072,8 +1072,8 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
                 QTAILQ_FOREACH(block, &ram_list.blocks, next) {
                     if (!strncmp(id, block->idstr, sizeof(id))) {
                         if (block->length != length) {
-                            error_report("Length mismatch: %s: " RAM_ADDR_FMT
-                                         " in != " RAM_ADDR_FMT, id, length,
+                            error_report("Length mismatch: %s: 0x" RAM_ADDR_FMT
+                                         " in != 0x" RAM_ADDR_FMT, id, length,
                                          block->length);
                             ret =  -EINVAL;
                         }