error: Replace qemu_error() by error_report()

error_report() terminates the message with a newline.  Strip it it
from its arguments.

This fixes a few error messages lacking a newline:
net_handle_fd_param()'s "No file descriptor named %s found", and
tap_open()'s "vnet_hdr=1 requested, but no kernel support for
IFF_VNET_HDR available" (all three versions).

There's one place that passes arguments without newlines
intentionally: load_vmstate().  Fix it up.
diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index c41ce9b..383240b 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -41,7 +41,7 @@
         }
     }
     if (dev->id >= bus->ndev) {
-        qemu_error("bad scsi device id: %d\n", dev->id);
+        error_report("bad scsi device id: %d", dev->id);
         goto err;
     }