test: Fix make target check-report.tap

Fix a fat-fingered invocation of tap-merge.pl in the recipe of target
check-report.tap.

Fixes: 9df43317 "test: replace gtester with a TAP driver"
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190604080010.23186-1-armbru@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>