usb: gadget: u_serial: remove some dead code

There is no need to check if "port" is NULL.  We already verified that it
is non-NULL.  It's a stack variable and can't be modified by a different
thread.  Delete this dead code.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Prashanth K <prashanth.k@oss.qualcomm.com>
Link: https://lore.kernel.org/r/685c1413.050a0220.1a8223.d0b9@mx.google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>