ahci: zero-initialize port struct

Specifically port->drive.lchs needs clearing, otherwise seabios will
try interpret whatever random crap happens to be there as disk geometry,
which may or may not break boot depending on how lucky you are.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

src/hw/ahci.c

@@ -345,6 +345,7 @@ ahci_port_alloc(struct ahci_ctrl_s *ctrl, u32 pnr)
         warn_noalloc();
         return NULL;
     }
+    memset(port, 0, sizeof(*port));
     port->pnr = pnr;
     port->ctrl = ctrl;
     port->list = memalign_tmp(1024, 1024);