powerpc/math-emu: Remove the dead code in math.c

The math.c is only built when CONFIG_MATH_EMULATION is enabled.
So we would never get into the case that CONFIG_MATH_EMULATION
is not defined in this file.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>