MIPS: math-emu: dsemul: Reduce `get_isa16_mode' clutter

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12178/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>