staging: et131x: Update tx trans_start on device close to prevent tx_timeout

Updating the tx trans_start before closing the device prevents a possible tx_timeout occuring during the closing process.
Tested on an ET1310 device.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>