backends/hostmem-epc: Get rid of qemu_open_old()

For qemu_open_old(), osdep.h said:

> Don't introduce new usage of this function, prefer the following
> qemu_open/qemu_create that take an "Error **errp".

So replace qemu_open_old() with qemu_open().

Cc: David Hildenbrand <david@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

backends/hostmem-epc.c

@@ -29,10 +29,8 @@ sgx_epc_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return false;
     }
 
-    fd = qemu_open_old("/dev/sgx_vepc", O_RDWR);
+    fd = qemu_open("/dev/sgx_vepc", O_RDWR, errp);
     if (fd < 0) {
-        error_setg_errno(errp, errno,
-                         "failed to open /dev/sgx_vepc to alloc SGX EPC");
         return false;
     }