set last opcode offset to the start of the opcode in cpu_restore_state

For ARM, cpu_restore_state() sets the program counter to the saved value at the offset of the last instruction.
We need to pass the offset of the start of the instruction, since that is the only array index that includes that data, instead of 0.
The code used for TCG should also be used for LLVM.

Example method of reproduction: NULL dereference in an ARM guest.