USB: serial: console: clean up sanity checks

USB: serial: console: clean up sanity checks

Drop two redundant NULL checks from usb_serial_console_disconnect().

The usb_serial_console_disconnect function is called from the
USB-serial-device disconnect callback when a device is going away. Hence
there is no need to check for the serial-device pointer being NULL.

The serial-device port pointers are stored in an array that is a member
of the serial struct so the address of the first member of the array
(which the array name decays to) is never NULL either.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
[sw0312.kim: backport upstream commit 0e517c93dc02 to resolve gcc-12 build issue]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: Ia32e9685c652ee25704be755fa5788bf93b16a82