test_fs: Rename mount dir to scratch

Since no mounting happens anymore, rename the "mnt"
directory to "scratch" and the related variables.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed