MIPS: Restore signalling NaN behaviour for abs.[sd]

Atsushi Nemoto <anemo@mba.ocn.ne.jp> spotted that this had been incorrectly
removed in a previous patch

Signed-off-by: Chris Dearman <chris@mips.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1213/


Tested-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>