sh: Fix TIF_USEDFPU clearing under FPU emulation.

The unlazy_fpu() path calls in to save_fpu() if the task has
TIF_USEDFPU set. save_fpu() being the crap API that it is has the side
effect of clearing the flag itself, which presently doesn't happen
if we're using FPU emulation. Fix this up for now, pending an overhaul
in 2.6.26.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>