Drop "qemu:" prefix from error_report() arguments

Drop "qemu:" prefix from error_report() arguments

error_report and friends already add a "qemu-system-xxx" prefix
to the string, so a "qemu:" prefix is redundant in the string.
Just drop it.

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <1537495530-580-1-git-send-email-maozhongyi@cmss.chinamobile.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Markus Armbruster <armbru@redhat.com>