fs-test.sh: Update expected result output

Given 0dc1bfb7 ("fs: fat: cannot write to subdirectories") we have
changed how the FAT code works from creating the illegal file "./file"
and instead rejecting the path.  The correct behavior would be to write
"file" to "." but not writing an illegal file is a step in the right
direction.  For now, update the expected output to account for the
failure.

Signed-off-by: Tom Rini <trini@konsulko.com>