Core/DSPCore: Make the JIT blocks return the number of cycles executed.
The block_size seems to be not reliable, even after trying to more closely match
the interpreter by looking at the analysis for (addr+opcode->size-1) for detecting
the end of the block.
Since we need to «calculate» this number shortly before returning to
RunForCycles, it seemed logical to use the (up to now) unused return value
of the blocks.
Improves SMG2 here.
Fix a bug introduced by r6240.
Fixes issue 3320.