usbip: Fix incorrect double assignment to udc->ud.tcp_rx

usbip: Fix incorrect double assignment to udc->ud.tcp_rx

Currently udc->ud.tcp_rx is being assigned twice, the second assignment
is incorrect, it should be to udc->ud.tcp_tx instead of rx. Fix this.

Fixes: 46613c9dfa96 ("usbip: fix vudc usbip_sockfd_store races leading to gpf")
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Cc: stable <stable@vger.kernel.org>
Addresses-Coverity: ("Unused value")
Link: https://lore.kernel.org/r/20210311104445.7811-1-colin.king@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>