Correct sceKernelSelfStopUnloadModule

Fix #4237
Init exitCode variable
Play it safer with savedata dialog thread safety.
Fire a callback when cpu mhz changes.

So these can adjust efficiently.  It's not like it changes often.
Reduce audio drift from 44.1kHz.

Although, not sure what the PSP's actual exact timing is...
Merge pull request #6482 from unknownbrackets/timing

Reduce timing inaccuracy from 44.1kHz
Use with same code with sceKernelStopUnloadSelfModuleWithStatus
Fix space bug
Reset the audio rate on save/load state.

Should fix #6484.
Also fire mhz change listeners on load state.
Merge pull request #6481 from sum2012/sceKernelModule

Correct sceKernelSelfStopUnloadModule