MIPS: math-emu: Work around limitations of older GCC.

Older GCC doesn't get named initializations of anonymous structs right,
that is members are not initializable in the containing structure through
name however old style initializations are working fine.

The issue exists with gcc up to 4.5.x.

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