[RISCV] Correct the CHECK prefixes in attr-riscv-rvv-vector-bits-globals.c to...

[RISCV] Correct the CHECK prefixes in attr-riscv-rvv-vector-bits-globals.c to use the correct vector size. NFC

These were copied from AArch64 where vscale is multiplied by 128
to get the vector length.  For RISC-V, vscale is multiplied by 64.