config/git: use flashprog instead of flashrom

Nico Huber is the rightful project lead. I do not support
the coup that occured within the flashrom project. Nico
has always been of great service to the Libreboot project,
by virtue of his work on both coreboot and flashrom.

Nico Huber was unfairly removed from the flashrom project
infrastructure, due to unfounded accusations hurled at him
by flashrom's new project lead. The accusations are unfounded
because no evidence was given.

Use Nico Huber's fork, named flashprog. We will work with
flashprog from now on.

Signed-off-by: Leah Rowe <leah@libreboot.org>