powerpc: Remove redundant clear of MSR_VSX in __giveup_vsx()

__giveup_fpu() already does it and we cannot have MSR_VSX set
without having MSR_FP also set.

This also adds a warning to check we indeed do

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/process.c

@@ -331,11 +331,19 @@ static inline int restore_altivec(struct task_struct *tsk) { return 0; }
 #ifdef CONFIG_VSX
 static void __giveup_vsx(struct task_struct *tsk)
 {
-	if (tsk->thread.regs->msr & MSR_FP)
+	unsigned long msr = tsk->thread.regs->msr;
+
+	/*
+	 * We should never be ssetting MSR_VSX without also setting
+	 * MSR_FP and MSR_VEC
+	 */
+	WARN_ON((msr & MSR_VSX) && !((msr & MSR_FP) && (msr & MSR_VEC)));
+
+	/* __giveup_fpu will clear MSR_VSX */
+	if (msr & MSR_FP)
 		__giveup_fpu(tsk);
-	if (tsk->thread.regs->msr & MSR_VEC)
+	if (msr & MSR_VEC)
 		__giveup_altivec(tsk);
-	tsk->thread.regs->msr &= ~MSR_VSX;
 }
 
 static void giveup_vsx(struct task_struct *tsk)