fs-test.sh: Correct check_md5() test with newlines

The fs-test.sh script expected there to be a \n\r style newline at the
end of the output. This is no longer the case, so use 'tr' to remove the
\r that we get.

Fixes: (c5917b4b "dm: serial-uclass: Move a carriage return before a
        line feed")
Signed-off-by: Tom Rini <trini@konsulko.com>