fs: remove distractive message in fs_read()

The message
"** %s shorter than offset + len **\n"
may be interesting when debugging but it does not indicate an
error.

So we should not write it if we are not in debug mode.

Fixes: 7a3e70cf fs/fs.c: read up to EOF when len would read past EOF
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>