The struct tty_port is part of the uart state and will never be NULL in
the receive helpers. Drop the bogus NULL checks and rename the
pointer-variables "port" to differentiate them from struct tty_struct
pointers (which can be NULL).

Fixes: 962963e4 ("serial: tegra: Switch to using struct tty_port")
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20200710135947.2737-3-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>