scsi virtio-blk usb-msd: Clean up device init error messages

Replace

    error_report("DEVICE-NAME: MESSAGE");

by just

    error_report("MESSAGE");

in block device init functions.

DEVICE-NAME is bogus in some cases: it's "scsi-disk" for device
scsi-hd and scsi-cd, "virtio-blk-pci" for virtio-blk-s390, and
"usb-msd" for usb-storage.

There is no real need to put a device name in the message, because
error_report() points to the offending command line option already:

$ qemu-system-x86_64 --nodefaults --enable-kvm -vnc :0 -S -monitor stdio -usb -device virtio-blk-pci
upstream-qemu: -device virtio-blk-pci: virtio-blk-pci: drive property not set
upstream-qemu: -device virtio-blk-pci: Device 'virtio-blk-pci' could not be initialized

And for a monitor command, it's obvious anyway:

$ qemu-system-x86_64 --nodefaults --enable-kvm -vnc :0 -S -monitor stdio -usb
(qemu) device_add virtio-blk-pci
virtio-blk-pci: drive property not set
Device 'virtio-blk-pci' could not be initialized

Reported-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
