drivers: tty: 68328serial.c: Do not initialize statics to 0

This patch removes an initialization of a static to 0 as checkpatch
suggests.

Signed-off-by: Frederik Völkel <frederik.voelkel@fau.de>
Signed-off-by: Lukas Braun <lukas.braun@fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>