ggml: bugfix: fix the inactive elements is agnostic for risc-v vector (llama/8748)

ggml: bugfix: fix the inactive elements is agnostic for risc-v vector (llama/8748)

In these codes, we want to retain the value that they previously held
when mask[i] is false. So we should use undisturbed. With the default
agnostic policy of rvv intrinsic, these values can be held or be
written with 1s.

Co-authored-by: carter.li <redacted>