sd/milkymist-memcard: Fix format string

Fixes: b98e8d12Signed-off-by: NStefan Weil <sw@weilnetz.de>
Message-Id: <20200722204054.1400555-1-sw@weilnetz.de>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NLi Qiang <liq3ea@gmail.com>
[Commit message tweaked]
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

hw/sd/milkymist-memcard.c

@@ -281,7 +281,7 @@ static void milkymist_memcard_realize(DeviceState *dev, Error **errp)
     carddev = qdev_new(TYPE_SD_CARD);
     qdev_prop_set_drive(carddev, "drive", blk);
     if (!qdev_realize_and_unref(carddev, BUS(&s->sdbus), &err)) {
-        error_propagate_prepend(errp, err, "failed to init SD card: %s");
+        error_propagate_prepend(errp, err, "failed to init SD card");
         return;
     }
     s->enabled = blk && blk_is_inserted(blk);