virtio.c: fix error message

Suggested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/virtio/virtio.c

@@ -440,7 +440,7 @@ void virtqueue_map_sg(struct iovec *sg, hwaddr *addr,
         len = sg[i].iov_len;
         sg[i].iov_base = cpu_physical_memory_map(addr[i], &len, is_write);
         if (sg[i].iov_base == NULL || len != sg[i].iov_len) {
-            error_report("virtio: trying to map MMIO memory");
+            error_report("virtio: error trying to map MMIO memory");
             exit(1);
         }
     }