fix including issue when using libchardet as a library

[lifegpc]

fix this including issue

[Neustradamus]

@Joungkyun: What do you think about this PR?

[Joungkyun]

@Neustradamus

I don't know the environment where that error occurs.
Is it building libchardet using the build environment of ffplay-starter?
I think I just need to add -I ../include to CPPFLAGS,
First of all, I've been waiting to do this patch together if there's another patch, but I haven't had another update distance for 4 years, so I'm waiting. It's a little ambiguous to update the version with just this.

In your opinion,

When you build alone, or when you build using the build environment of another program, do you think this patch satisfies both conditions enough?