staging: speakup: use native error codes

The mapping as follows:
	E_RANGE		-> ERANGE
	E_UNDEF		-> ENODATA
	E_TOOLONG	-> E2BIG
	SET_DEFAULT	-> ERESTART

As a side effect it fixes a bug in spk_var_store() where return code was
mistakenly compared to negative value instead of positive.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>