drivers/dahdi/dahdi-base: fix linux 7.1 compat
Adjust to the "code" argument of ppp_input_error() not existing anymore
since abb0eb0b ("ppp: simplify input error handling").
Related: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=abb0eb0b033a0a8980eb9215e02626e4801ead3f
Change-Id: Ia17190e4bd8bcc480cbe98b55f930149e554a576