Fix incorrect comment in Bytecode.h

[mttsner]

The description of SUBRK/DIVRK is out of sync with the VM code.

Comment:

// SUBRK, DIVRK: compute arithmetic operation between the constant and a source register and put the result into target register
// A: target register
// B: source register
// C: constant table index (0..255); must refer to a number
LOP_SUBRK,
LOP_DIVRK,

VM snippet:

VM_CASE(LOP_DIVRK)
    {
        Instruction insn = *pc++;
        StkId ra = VM_REG(LUAU_INSN_A(insn));
        TValue* kv = VM_KV(LUAU_INSN_B(insn));
        StkId rc = VM_REG(LUAU_INSN_C(insn));
        ...