staging: fwserial: fix resource leak

staging: fwserial: fix resource leak

This patch fixes the leak, which was present in fwserial driver in the
init function. In case the tty driver allocation failed the function
returned error, leaving debugfs entry in the filesystem.

To fix the issue additional error label was added, so that the code will
jump to it in case of allocation failure, and free debugfs entries.

Signed-off-by: Vladimirs Ambrosovs <rodriguez.twister@gmail.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>