First, it's probably not useful to arbitrarily claim what the biggest flaw in the design of C is without context or data.
Second, I don't think it's reasonable in this case to place the blame on the design of a language (certainly, the choice of C has long been a pragmatic decision). As Linus alludes to directly, the tools exist with which to write more correct, idiomatic C code for the kernel (e.g., ARRAY_SIZE and a useful gcc warning).
Finally, as the historical record should demonstrate, 'getting rid of X by replacing it with Y' is not particularly actionable; it certainly isn't the most efficient solution in terms of resources and likely not in terms of correctness over the short- to medium-term.
If I'm to hazard a guess, the point of his message was to remind everyone the biggest source of flawed code lies in our own hands and in the biases individuals and groups bring to large-scale development.
The choice, here, isn't between using a good language and a bad language; it's between using a language and its idioms correctly, and using those things lazily with foul consequences.