math-emu: Fix compiler warnings

Fix warnings of the form:
arch/powerpc/math-emu/fsubs.c:15: warning: 'R_f1' may be used uninitialized in this function
arch/powerpc/math-emu/fsubs.c:15: warning: 'R_f0' may be used uninitialized in this function

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>