lib: fix ubsan errors in cbvprintf_package

It is undefined behaviour to shift / add offsets to a null pointer.

Move to direct offset tracking to satisfy UBSAN.

Simple translation of code:
buf0 -> buf
buf +=/++ -> offset +=/++
buf = -> buf+offset =

Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
1 file changed