Update the upstream URL to 'ggml-org' organization

This month, the upstream project moved its repository from:

    https://github.com/ggerganov/whisper.cpp.git

to:

    https://github.com/ggml-org/whisper.cpp.git

Update the submodule URL accordingly.

Signed-off-by: Fujimoto Seiji <fujimoto@ceptord.net>