coverity-model: replay data is considered trusted

Replay data is not considered a possible attack vector; add a model that
does not use getc so that "tainted data" warnings are suppressed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20180514141218.28438-1-pbonzini@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Whitespace tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>