powerpc/mm: Avoid double irq save/restore in activate_mm

It calls switch_mm() which already does the irq save/restore
these days.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/mmu_context.h

@@ -176,11 +176,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
  */
 static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)
 {
-	unsigned long flags;
-
-	local_irq_save(flags);
 	switch_mm(prev, next, current);
-	local_irq_restore(flags);
 }
 
 /* We don't currently use enter_lazy_tlb() for anything */