powerpc: Remove the redundant flush_fp_to_thread() in setup_sigcontext()

In commit c6e6771b(powerpc: Introduce VSX thread_struct and CONFIG_VSX)
we add a invocation of flush_fp_to_thread() before copying the FPR or
VSR to users. But we already invoke the flush_fp_to_thread() in this
function. So remove one of them.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/signal_64.c

@@ -96,8 +96,6 @@ static long setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs,
 	unsigned long msr = regs->msr;
 	long err = 0;
 
-	flush_fp_to_thread(current);
-
 #ifdef CONFIG_ALTIVEC
 	err |= __put_user(v_regs, &sc->v_regs);