Correct sandbox filesystem commands in FIT image test

The host filesystem name has changed, so update the tests. The tests now
run again correctly:

$ make O=b/sandbox sandbox_defconfig all
...
$ test/image/test-fit.py -u b/sandbox/u-boot
FIT Tests

=========
Kernel load
Kernel + FDT load
Kernel + FDT + Ramdisk load

Tests passed
Caveat: this is only a sanity check - test coverage is poor

Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed