Correct the instruction flags of RISC-V vector store instructions, such
as `vse64_v`, `vse32_v`. The `vse64_v` in `decoder.isa` is
`Mem_vc.as<uint64_t>()[i] = Vs3_ud[i];` and it will generate the code
`Mem.as<uint64_t>()[i] = Vs3[i];`. The current regex of assignRE only
mark the operand `Mem` as `dest` only if meet the formats like `Mem = Rd`
or `Mem[i] = Rd` because the code ` = Rd` or `[i] = Rd` match the
`assignRE` respectively. For the expression `Mem.as<uint64_t>()[i]`,
the operand `Mem` will falsely mark the operand as `src` because the
code `.as<uint64_t>()[i]` is not match the `assignRE`.
The PR will ensure the operand `Mem` is dest for the format like
`Mem.as<xxx>()[i] = yyy`.
Change-Id: I9c57986a64f1efb81eb9c7ade90712b118e0788d
bedc3c597c