The db_assert call checks whether the bus_num pointer is non-NULL, but
does so after said pointer has been dereferenced by the assignment on
the previous line. Thus the check is pointless & likely to have been
optimised out by the compiler anyway. The check_args function is static
& only ever called from the local file with bus_num being a pointer to
an on-stack variable, so the check seems somewhat overzealous anyway.
Simply remove it.