mpeg: dvbpsi: avoid casting callbacks
The function signature does not match the dvbpsi callback (demux_t* instead of void*). While this is supported by many platforms and compilers, it's undefined behavior strictly by the standard [1] and it's known to often fail with emscripten 1.
[1]: Section 6.3.2.3, paragraph 8:
A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function whose type is not compatible with the pointed-to type, the behavior is undefined.
Quoting section 6.7.5.1, paragraph 2 for pointer compatibility:
For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types.