configfs: Return -EFBIG from configfs_write_bin_file.

The check for writing more than cb_max_size bytes does not 'goto out' so
it is a no-op which allows users to vmalloc an arbitrary amount.

Fixes: 03607ace ("configfs: implement binary attributes")
Cc: stable@kernel.org
Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>